Formatting.

Also had the wrong type in the no-op collection view controller's
-themeCell:atIndexPath:.
Revert "Prevent following a link after a long press to show the share sheet."

This actually prevents selections from working. And it's no longer needed since
reverting the share sheet changes.

This reverts commit 29445dbaba2a105a8e66ed47d3b371cc08777671.
Don't pop sidebar navigation when swiping to reveal sidebar.

I was occasionally seeing a single "swipe to reveal sidebar" gesture also
popping the navigation controller. Moving the swipe-to-pop gesture recognizer
to the cover view makes more sense conceptually, and comes with the added
benefit of not needing to check whether the swipe was actually over the detail
view.