reauth: check for updated oauth tokens, update if necessary

[eriktaubeneck]

Added test for coverage for this change. Test passes for SQLAlchemy app, but not for MongoDB or Peewee apps. The after_this_request(_commit) doesn't seem to take for those two, and I'm not sure exactly how to add the updated connection object to the abstracted "session" (or if that even makes sense in this abstraction).

[eriktaubeneck]

Also, need to update the other providers before this is merged in, but wanted to get feedback first.

[eriktaubeneck]

Also 2, plan to add a /reauth (or equivalent) route, which would log the user out, then log them back in through the account that needs reauting, resulting in a reauth, unless anyone sees a cleaner way to do that.

[eriktaubeneck]

I've added the get_token_pair_from_response method to all providers, added the /reconnect/<provider_id> route, and written a test to cover the new route. The mongo and peewee tests are still failing, (now on both tests).

[eriktaubeneck]

Doh. I needed to add _datastore.put(connection) after it was updated. I'm actually confused as to why the SQLAlchemyDatastore tests passed without that, particularly because I just tested it in the wild and it didn't work. WIth that change, all tests are passing. Testing in the wild currently.

[jaitaiwan]

@eriktaubeneck Anything you need help with on?