Allow to Customize the 'Add' dialogs Merged

Right now it is necessary to navigate between multiple different screens before you can add to the system a To-Do or Activity entity.

It should be possible to customize the 'Add' dialogs to include additional fields so that a user can complete the creation easily from a single screen.

Fields that should be available for addition:

1. Links to the higher level entities  ( i.e. for a To-Do, allow linking to an activity, epic or release, for an activity - allow linking to an initiative or/and epic etc) 

2. Assignee 

3. Status

4. etc