Refine Swift usage with fatal errors.

Use instead of comments for required overrides of
FormViewController.
Add minor Swift style tweak for switch blocks.
Continue refactoring and dieting EventViewController.

Migrate data binding logic, which includes
implementing input delegate methods. Currently
only used input view types are supported.

Also make the KVO context constant shared, since
it's tricky to create one per file. Not ideal, but
enough for this app.

Minor cleanup included.