[x] Revamp the settings page to make it easier to find things
[x] Alert the user to how the push notification interceptor works, if they select that option.
[x] Changes to activity refresh:
Only give mention notifications if the standalone mention background refresh is turned off
If it is turned on, and the activity refresh picks up a new mention, then just start a mention refresh service (this service provides much richer notifications
[x] Add a notification listener service
Whenever a notification comes in from Twitter, just kick off the activity refresh
This will be for #67.