Fix Months screen title animated setting...

Animated setting was being improperly guarded.
mainLabel doesn't get set until animation
completion, so it can't be used to check for
redundant values. Use interstitialLabel instead.
Fix Months screen title animation quality...

If an animation is already running, the new
animation cancels the previous one but starts from
the modelLayer value, not the presentationLayer's.
So the animation jumps. iOS8 has the API fixes;
the current solution's to mitigate the jump by
letting the current animation finish by a safe
(though noticeable) margin using dispatch_after
and a new animatingText flag.