Implement pagination, order by and groups in search

Fix tox config after fa1cf5ef

Retry dead servers a lot less often

Squash-merge of PR #345 from daniel/anonymousevents

Remove fields that are both unspecified and unused from the filter checks

This follows the same flows-based flow as regular registration, but as
the only implemented flow has no requirements, it auto-succeeds. In the
future, other flows (e.g. captcha) may be required, so clients should
treat this like the regular registration flow choices.

Remove unused arguments and code

Conflicts:
	synapse/notifier.py

Remove the LockManager class because it wasn't being used

Remove fields that are both unspecified and unused from the filter checks, check the right top level definitions in the filter

Include read receipts in v2 sync

Fix broken cache for getting retry times.

Conflicts:
	synapse/handlers/sync.py

Add APIs for adding and removing tags from rooms

Fix broken cache for getting retry times. This meant we retried remote destinations way more frequently than we should

Add missing column