R1:ad382b3abe8f

Mobile fix for creating another task UI

Summary: Makes the layout more useful on mobile. Fixes T3042

Test Plan: Review layout on mobile.

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T3042

Differential Revision: https://secure.phabricator.com/D7860