Remove unnecessary Crashlytics logging.

I think we've fixed the profile problems, and the crash was happening before
these logging calls anyway.

Bonus: add __PRETTY_FUNCTION__ to the second log.
Rework how split view handles detail view when master view is open.

This way we're not messing with the userInteractionEnabled of views we don't
own.
Minor VoiceOver improvements.

* Tabs have a useful accessibility label.
* Button cells in the settings table have the button trait.
* When the sidebar is open on iPad, the non-sidebar has a "double-tap to
  dismiss sidebar" hint.
Mimic Mail.app's split view's continuous swipe gesture.

You can peek at the sidebar by swiping right, not lifting your finger, then
swiping back left.

Bonus: include tgmath in prefix for CGFloat-overloaded math functions.