Refine Swift usage...

Use the '+=' shortcut for array append.

Tweak if's and if-let's.

Force unwrap on dictionary access subscript to
obviate bridging to NSDictionary. Also work around
inability to chain forced unwraps in these cases.
Reorder MonthsViewController and section properties.
Add initial port of MonthsViewController add event extension.
Complete port of MonthsViewController title view extension.
Complete port of MonthsViewController layout extension.