Reintroduce batch Collections operation via metadata panel

[paperboyo]

Short description

Since #3465, we may have lost the ability to edit Collections via metadata panel for when more than one image is selected. The only way to do that is by dragging. We should introduce this device available for one image to operate on selections of multiple too:

This may be of help, but it would be great if the design of it would follow the current control and not look like editing Persons, Labels etc.