SCST tokens are now stored in the 'tokens' table.
This unifies old token handling and new subclient-specific tokens.
Also ensures the BlenderID expiry of the token is taken into account.
Removes use of httpretty, in favour of responses.
WARNING: make a backup copy of your local config.py before pulling
this change, as Git will overwrite it without warning.
The configuration defaults to deployment settings, allowing overrides.
Overrides are read from config_local.py and from the file pointed to
by the PILLAR_CONFIG env var.
