Extension:ImageTweaks/UI

We should design and develop the interface for this extension so that its modular. It should be usable both from its special page and as a dialog. That'll make integration with VE (if ever) easier and also give us the option to load a dialog as soon as someone clicks Edit Image from the toolbox.

The specifics of the API are slightly foggy. We aren't yet sure which service we'll be using and thus what limitations we might have to put in the interface and the user. Even without the technical limitations we don't intend to make a replacement for desktop image editing tools. Editors have some common actions they perform on images, and they'll trust an online tool for only a subset of those actions. Trying to find out what those actions are is essential in making this tool useful.

As this is still an experiment, we could focus on a small set of tools and a clean interface. Integrating a highly visible feedback mechanism in the interface for surveying editors about the tools they want to see will tell us what to work on next (we could use EL for this? but its technically a survery, so…). The bare minimum set of tools could be:
 * Crop
 * Rotate, only by factors 90° (this will eliminate the weird background color issue)
 * Flip vertical & horizontal (maybe)