New import modes of bin and prg

[GoogleCodeExporter]

Being able to import multiple bin or prg data to an existing image.

Recreate an image from various components like separate bitmap, screen and 
color.

Should work for chars or sprites as well.

Suggested workflow:
1. Create an empty image (any format).
2. Select a component like bitmap and merge it.
3. repeat step 2 for screen or color file.

Original issue reported on code.google.com by [email protected] on 22 Feb 2014 at 10:22