Fix reloading thread cells after downloading new thread tags.

Removing all objects before using them is pretty pointless.
Remove gap at bottom of compose view when dismissing keyboard.
Confirm cancelling a new thread if subject or text was written.
Whiten new thread button on iPad.
Fix crash showing thread action sheet from a thread list on iPad.
Fix crash when toggling a favorite forum added or removed the Favorites section.

I couldn't reproduce this crash, and I'm astounded it doesn't happen every
time. It happens because, in a UITableView beginUpdate/endUpdate block, reloads
use the index paths of cells *before* any section or row deletions. The index
path was incorrectly accounting for this section insertion/deletion.