MEDIA BROWSER: Shift + click not following OS conventions

Shift + click should select all media items between the first-selected clip and second-selected clip in the library. Shift currently acts as Ctrl should (adding one single element to the selection at a time). Also, drag-select should be added (allowing to shift drag to add different group clusters to the selection). Currently, deleting a lot of media clips from the project is very difficult and requires clicking each one individually. With many files being generated in the project (through renders, etc.), this is problematic.