Split "Create Another Task" button into "Similar Task" and "Empty Task"

Summary: Looping on this interface is pretty useful but you don't always want to
keep the projects/owners.

Test Plan: Clicked both buttons.

Reviewers: btrahan

Reviewed By: btrahan

CC: anjali, aran, epriestley

Differential Revision: https://secure.phabricator.com/D1593