First pass at event modal create options.
Summary: Ref T8568, First pass at event modal create options.
Test Plan: Calendar → Create should offer three options: Create Event, Create Public Event, Create Recurring Event.
Reviewers: epriestley, #blessed_reviewers
Reviewed By: epriestley, #blessed_reviewers
Subscribers: epriestley, Korvin
Maniphest Tasks: T8568
Differential Revision: https://secure.phabricator.com/D13309