Added support for refreshing the device list, marking current device with a checkmark instead of a lock

- add missing mimetype
- allow removal of images from pack
- allow GIF as a format
- don't divide size by 2 if the image is very small already

We explicitly set a parent. We can't assign to
ApplicationWindow.transientParent though, only to
Window.transientParent, so we just call setTransientParent in C++.