Fix broken navigation from Months to Day screen.

The situation:

NavigationController calls EventManager's
completeSetup for each view controller load,

which calls EventKit's requestAccessToEntityType,

which notifies Months screen,

which calls NavigationTitleScrollView's
refreshSubviews,

which re-renders the scroll view and triggers
scrollViewDidScroll, 

which fails to get header layout attributes
probably due to the transition in progress.
Minor Months screen hardening and cleanup.