Remove test target memberships to fix syntax highlighting.

In Xcode-6-b4, SourceKit seems to fail when swift
sources are also members of the test target.
Complete port of MonthsViewController navigation extension.

Includes further filling in ZoomTransitionCoordinator.
Add initial port of MonthsViewController collection view extensions.

Also stub DayViewCell and MonthHeaderView.
Fix minor Swift style inconsistency.