The main advantage of SPDX license identifiers over the traditional
license headers is that it's more difficult to overlook inappropriate
licenses for kwin, for example GPL 3. We also don't have to copy a
lot of boilerplate text.
In order to create this change, I ran licensedigger -r -c from the
toplevel source directory.
When an application is not responding, its window is desaturated to communicate this.
Also "(Not Responding)" is added to the title bar.
Differential Revision: https://phabricator.kde.org/D5245
