Tidy up AwfulThreadCell long-press action handling.

Gesture recognizer is an implementation detail.
Formatting.
Move view controller getter out to category on UIView.
Tidy up AwfulFrameworkCategories.h.

* Forgot UIColor category.
* Alphabetize.
Rewrite thread tag picker.

The new picker is simpler as it just takes an array of image names (plus an
optional array of secondary image names). The delegate no longer needs to
supply images.

In addition, the secondary tags are more nicely drawn in the picker. The
checkmark seemed superfluous with the filled-in background (plus it obscured
the title text). And the title text has more room to breathe.