Move rest APIs back under the rest directory

synapse/app/homeserver.py

synapse/rest/__init__.py

synapse/rest/client/__init__.py

synapse/rest/client/v1/__init__.py

synapse/rest/client/v1/admin.py

synapse/rest/client/v1/base.py

synapse/rest/client/v1/directory.py

synapse/rest/client/v1/events.py

synapse/rest/client/v1/initial_sync.py

synapse/rest/client/v1/login.py

synapse/rest/client/v1/presence.py

synapse/rest/client/v1/profile.py

synapse/rest/client/v1/register.py

synapse/rest/client/v1/room.py

synapse/rest/client/v1/transactions.py

synapse/rest/client/v1/voip.py

synapse/rest/media/__init__.py

synapse/rest/media/v0/__init__.py

synapse/rest/media/v0/content_repository.py

synapse/rest/media/v1/__init__.py