RequireFieldsApp: remove unused "type2thing"
RequireFieldsApp: rename typeII to "toggleSave"

Additionally, the app.activated event triggered setValue, which in turn
just called typeII. Now it points directly to toggleSave.
RequiredFieldsApp: extract some helper methods

 * Make fieldValueIsBlank and anyValueIsBlank closure-local functions
 * Add App#checkedFieldValues that returns the current values of the
   checked fields.
Merge pull request #2 from skipjac/required_fields_cleanup

RequiredFieldsApp: some cleanup