R1:a16e8773f009

Show confirmation dialog when closing a modal if form contents have been changed

Summary: Honestly I did not realize that Differential can do this. Anyway this is related to T15034 ... Originally opened at https://secure.phabricator.com/T12676

Test Plan:
1) Start creating a task via a Workboard in Manifest, type many words, press `ESC`

2) Start creating a task via a Workboard in Manifest, type no words, press `ESC`

Reviewers: O1 Blessed Committers, Ekubischta, speck

Reviewed By: O1 Blessed Committers…