SYN-67: Finish up implementing new database schema management

synapse/app/homeserver.py

synapse/storage/__init__.py

synapse/storage/schema/current/11/event_edges.sql

synapse/storage/schema/current/11/event_signatures.sql

synapse/storage/schema/current/11/im.sql

synapse/storage/schema/current/11/keys.sql

synapse/storage/schema/current/11/media_repository.sql

synapse/storage/schema/current/11/presence.sql

synapse/storage/schema/current/11/profiles.sql

synapse/storage/schema/current/11/redactions.sql

synapse/storage/schema/current/11/room_aliases.sql

synapse/storage/schema/current/11/state.sql

synapse/storage/schema/current/11/transactions.sql

synapse/storage/schema/current/11/users.sql

synapse/storage/schema/delta/11/v11.sql

synapse/storage/schema/delta/12/v12.sql

synapse/storage/schema/delta/13/v13.sql

synapse/storage/schema/delta/14/upgrade_appservice_db.py

synapse/storage/schema/delta/v2.sql

synapse/storage/schema/delta/v3.sql