Add exposure slider

[clodman84]

the ImageWindow should support basic editing

We take thousands of pictures and some images have visual defects. It would be nice to have a way to edit the images being taken to be easily edited during the process to prevent sub-par images being billed to students. Since we take most of our images in direct sunlight a lot of them are over exposed. Therefore an exposure control should be the first image editing feature we should implement. Here are some examples of images that could be improved:

how should this be implemented

A slider in the image window is probably the best way to do this, however the changes that need to be made within the internals of the app are not super straightforward. Still very doable though