Is your feature request related to a problem? Please describe.
After capturing a screenshot to the clipboard, I'd like to be able to close the ksnip window quickly via a keyboard shortcut, without having to move the mouse to click a small icon to close it. (See Fitts's law which explains why having to do that is bad).

Describe the solution you'd like
I'd like a simple keybinding for closing the window - ideally Escape since that's both logical and conventional for many other apps, but it could also be configurable if for some reason others don't like that binding.