Retain collision data even when background image size changes

[paxperscientiam]

Is your feature request related to a problem? Please describe.
As of v4.1.3 on macos, Game Boy Studio (GBS) nukes the collision data for a scene whenever the size of the background image changes. This is annoying because the work of laying out collision elements is lost in the event where the background image size is changed for, say, creative reasons

Describe the solution you'd like
GBS should not delete collision elements when the size of a scene's background image is changed.

Describe alternatives you've considered
GBS should retain mapping of collision elements with respect to a coordinate system that maps the top-left of the scene to the top-left of the background image.

[nielsderijk]

Same for palette assignments on tiles.

[chrismaltby]

That's a good point I've just made this fix 48a93aa to address the issue (for both collisions and color data)

Like you suggested it maps using the top left corner as an origin, if you reduce the size of the background image the collision/color data will now be cropped and if you increase the size of the image it will add blank tiles to the right and bottom keeping everything in the top left as it was.

[paxperscientiam]

@chrismaltby that sounds amazing! Thank you :)