Merge pull request #817 from matrix-org/dbkr/split_out_auth_handler

synapse/handlers/__init__.py

synapse/handlers/register.py

synapse/rest/client/v1/login.py

synapse/rest/client/v2_alpha/account.py

synapse/rest/client/v2_alpha/auth.py

synapse/rest/client/v2_alpha/register.py

synapse/rest/client/v2_alpha/tokenrefresh.py

synapse/server.py

tests/rest/client/v2_alpha/test_register.py

tests/utils.py