Move static Day screen layout attributes into IB.
Switch event cell text to attributed to change line height.
Refine Swift usage and reduce if-let's in DayViewController.
Simulate auto-resizing event cell heights.

Using a 'sizing-cell' seems like a pain and even
more so with storyboards. The new estimatedSize
API auto-resizes both dimensions. This calculation
simply estimates the height based on the content
length. It's good enough for now.