Improvement to the pin tool

Currently flameshot provides a simple implementation of image pinning. However, this implementation is quite simple. Once the image is pinned, it floats at the top of the desktop and can be dragged around, but that's basically everything. In order to close this pinned image, one will have to use the "Esc" key or double click on the image. Otherwise the only possible way is to close from the window list. This is not friendly to tablet users who have limited access to the keyboard.

I think the following improvements can be made:

• Allow right click on the pinned image; a menu should pop out giving options to close the pinned image or save it as an image file on disk.
• Document the usage of pin tool somewhere. I doubt users ever know the behavior of "double click to close".