Extract the client v1 base RestServlet to a separate class

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/voip.py