Add a 'has_consented' template var to consent forms

Fix dependency on jinja2

fixes #3260

... to reduce the risk of somebody introducing an html injection attack...

Delay the import of ConsentResource, so that we can get away without jinja2 if
people don't have the consent resource enabled.

Fixes #3259

Reject attempts to send event before privacy consent is given

Returns an M_CONSENT_NOT_GIVEN error (cf
https://github.com/matrix-org/matrix-doc/issues/1252) if consent is not yet
given.

Send users a server notice about consent

... and have the sync endpoints call it directly rather than obsure indirection
via PresenceHandler

turns out we need to reuse this, so it's better in the config class.

When a user first syncs, we will send them a server notice asking them to
consent to the privacy policy if they have not already done so.

we're going to use it for the version we require too.

Fix logcontext resource usage tracking

Add in flight request metrics

Stop the transaction cache caching failures

Tighter filtering for user_daily_visits

ONE DAY I WILL PURGE THE WORLD OF THIS EVIL

The transaction cache has some code which tries to stop it caching failures,
but if the callback function failed straight away, then things would happen
backwards and we'd end up with the failure stuck in the cache.

Add lxml to docker image for web previews

This tracks CPU and DB usage while requests are in flight, rather than
when we write the response.

fix psql compatability bug

Signed-off-by: Paul Tötterman <paul.totterman@iki.fi>

Changes in synapse v0.29.1 (2018-05-17)
==========================================
Changes:

* Update docker documentation (PR #3222)

Changes in synapse v0.29.0 (2018-05-16)
===========================================
Not changes since v0.29.0-rc1

Changes in synapse v0.29.0-rc1 (2018-05-14)
===========================================

Notable changes, a docker file for running Synapse (Thanks to @kaiyou!) and a
closed spec bug in the Client Server API. Additionally further prep for Python 3
migration.

Potentially breaking change:

* Make Client-Server API return 401 for invalid token (PR #3161).

  This changes the Client-server spec to return a 401 error code instead of 403
  when the access token is unrecognised. This is the behaviour required by the
  specification, but some clients may be relying on the old, incorrect
  behaviour.

  Thanks to @NotAFile for fixing this.

Features:

* Add a Dockerfile for synapse (PR #2846) Thanks to @kaiyou!

Changes - General:

* nuke-room-from-db.sh: added postgresql option and help (PR #2337) Thanks to @rubo77!
* Part user from rooms on account deactivate (PR #3201)
* Make 'unexpected logging context' into warnings (PR #3007)
* Set Server header in SynapseRequest (PR #3208)
* remove duplicates from groups tables (PR #3129)
* Improve exception handling for background processes (PR #3138)
* Add missing consumeErrors to improve exception handling (PR #3139)
* reraise exceptions more carefully (PR #3142)
* Remove redundant call to preserve_fn (PR #3143)
* Trap exceptions thrown within run_in_background (PR #3144)

Changes - Refactors:

* Refactor /context to reuse pagination storage functions (PR #3193)
* Refactor recent events func to use pagination func (PR #3195)
* Refactor pagination DB API to return concrete type (PR #3196)
* Refactor get_recent_events_for_room return type (PR #3198)
* Refactor sync APIs to reuse pagination API (PR #3199)
* Remove unused code path from member change DB func (PR #3200)
* Refactor request handling wrappers (PR #3203)
* transaction_id, destination defined twice (PR #3209) Thanks to @damir-manapov!
* Refactor event storage to prepare for changes in state calculations (PR #3141)
* Set Server header in SynapseRequest (PR #3208)
* Use deferred.addTimeout instead of time_bound_deferred (PR #3127, #3178)
* Use run_in_background in preference to preserve_fn (PR #3140)

Changes - Python 3 migration:

* Construct HMAC as bytes on py3 (PR #3156) Thanks to @NotAFile!
* run config tests on py3 (PR #3159) Thanks to @NotAFile!
* Open certificate files as bytes (PR #3084) Thanks to @NotAFile!
* Open config file in non-bytes mode (PR #3085) Thanks to @NotAFile!
* Make event properties raise AttributeError instead (PR #3102) Thanks to @NotAFile!
* Use six.moves.urlparse (PR #3108) Thanks to @NotAFile!
* Add py3 tests to tox with folders that work (PR #3145) Thanks to @NotAFile!
* Don't yield in list comprehensions (PR #3150) Thanks to @NotAFile!
* Move more xrange to six (PR #3151) Thanks to @NotAFile!
* make imports local (PR #3152) Thanks to @NotAFile!
* move httplib import to six (PR #3153) Thanks to @NotAFile!
* Replace stringIO imports with six (PR #3154, #3168) Thanks to @NotAFile!
* more bytes strings (PR #3155) Thanks to @NotAFile!

Bug Fixes:

* synapse fails to start under Twisted >= 18.4 (PR #3157)
* Fix a class of logcontext leaks (PR #3170)
* Fix a couple of logcontext leaks in unit tests (PR #3172)
* Fix logcontext leak in media repo (PR #3174)
* Escape label values in prometheus metrics (PR #3175, #3186)
* Fix 'Unhandled Error' logs with Twisted 18.4 (PR #3182) Thanks to @Half-Shot!
* Fix logcontext leaks in rate limiter (PR #3183)
* notifications: Convert next_token to string according to the spec (PR #3190) Thanks to @mujx!
* nuke-room-from-db.sh: fix deletion from search table (PR #3194) Thanks to @rubo77!
* add guard for None on purge_history api (PR #3160) Thanks to @krombel!

Infrastructure for a server notices room

Fix error in handling receipts