Factor out a CollectionViewTileCell class.

Make the customized UI aspects available for other
cells to use.
Cleanup day cell setup debris.
Allow tile cell depress animation to handle rectangles.

Amount depressed should be equal on all sides.
Factor aspect ratio into the scale delta (depress
depth) calculation.
Turn event cell into a tile cell.
Refine Swift usage by using strict equality when appropriate.
Allow EventViewController to update with pre-existing event.

Update FormViewController with the base update
method and refactor data object keys into a
value-input-view key-paths map.

Then re-integrate with FormViewController. Add
method for getting the day-menu item from a date.
Clean up day-menu code.

Also refine the public interface for TitleScrollView.
Fix day-menu button items preventing scrolling.
Link Day screen to event editing.

Does not include dismissal. Minor cleanup included.