Make the editor image selection popup list scrollable

[Robyt3]

Make the editor image selection popup list scrollable with a CScrollRegion to support maps with many images.

The width of the popup and list are also increased to support images with longer names.

Editor world/map scrolling with the mouse wheel is disabled while a popup is active, to better support popups with scrollable content.

Before:

After:

[ChillerDragon]

Oy decline incoming due to being old editor :/