Make TaskViews editable

The fields in a task view can now be edited by the user. To listen for input,
the presenter can register an "on save" and "on reload" listener where it can
read or update the fields appropriately.

Change-Id: If31f50be621c6a5ac9dda9caf2e8e18cbd2b3559
Merge "Make TaskViews editable" into feature/tasks