Implement an "existing product group" picker in Group Products dialog,
Additional info
Fixes #648
Testing notes:
Press CTRL+G in loader to get the Group Products dialog
If the current folder has any existing product groups - clicking button right hand side in pop-up should list them for you to easily "put it into that group"
if the current folder has no existing product groups - the button right hand side should be disabled.
Changelog Description
Implement an "existing product group" picker in Group Products dialog,
Additional info
Fixes #648
Testing notes: