Add way to reload all images

[spillerrec]

To make it easier to make changes to preprocessing options, add a way to reload all images.

[spillerrec]

Also keep track of the alpha mask, we only want to have one in memory, instead of a copy for each image which uses one. Make it work with the alpha additions to AImageAligner.

[spillerrec]

This has pretty much been solved by the new system.