Overhaul automatic refreshing.

* Keep track of last refresh times app-wide in AwfulRefreshMinder.
* Update user info occasionally when going into the basement.
* Throttle checking for a new avatar image.
* Throttle user info update when going into Settings.
* Consistently name method -refreshIfNecessary.
* Consistently call -refreshIfNecessary from -viewDidAppear:.
Formatting.
Only notify about a settings change if the setting changes.

Pasting over an identical value isn't worth notifying.
Stop username atop basement from animating into view.