Editor: Enhance object selection window to show more objects at the same time

Preliminary checks

• I've checked that there aren't other open issues on the same topic.

Describe the problem requiring a solution

Currently, the object selection popups contain 1:1 scale pictures of the objects, which makes browsing troublesome - especially on low resolution settings. For example for original 640x480 res, there are only TWO objects at the same time (except units and resources where 4-5 of them match in the window) - see the attached picture:

Describe the possible solution

Make the object icons smaller (but not as small as in the original editor :P) AND/OR show them in some kind of 2D grid instead of list

Additional info

1.1.0 on Android 5.1.1