These functions set the correct Content-Type header when JSON is given,
add a resp.json() function that also checks the response mime type,
and adds the correct Authorization header.
For unauthenticated/non-subscriber users, image file documents retain
their variations. All other documents have ther variations stripped.
Also the links + expiry info to the original file are removed for all
file types.
This gives us much more concrete information when a test fails.
Note that this info is generally put into the HTTP response data,
and not logged to any logger.
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.
