Measurable Ratings: Allow applications to be mapped from the measurable screen

[davidwatkins73]

Rather than map to measurables from an application (forcing you to use the trees) we could allow for users to (bulk) map from the measurable item to a bunch of applications (taking the default ratings).

[davidwatkins73]

The widget for selecting apps used in the app-group admin screen could be a good starting point.

[rovats]

Would also be very useful to allow apps to be mapped individually, so that users can select ratings for each app separately.

[jessica-woodland-scott-db]

See #4382