Issuable form due date
For some reason, this was never in the original merge request for due date?
![Screen_Shot_2016-04-22_at_21.49.44](/uploads/7d4e2b07f75a33009e3170fdb076a4bd/Screen_Shot_2016-04-22_at_21.49.44.png)
Closes#15516
See merge request !3895