Automatic social media connect

## New features

* Connect a section to a Twitter account with one button
* Connect a section to a Facebook account with one button
* Sections now have a flag that enables/disables bit.ly shortening so it can be turned on/off by section

Note that in order for the Twitter/Facebook connection to work, each network's app's key/secret must be configured in the database.

## Steps to upgrade

1. upgrade requirement: facepy was updated
1. migrate the database (`python manage.py migrate scheduler`): a flag in Section was added to toggle shortening links
1. and run the init script (`python manage.py init`): Facebook app ID/secret are now needed