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.
Shaders are moved into dedicated directories 1.10 and 1.40. 1.10 contains
the already existing versions, 1.40 copies of them adjusted to GLSL 1.40.
REVIEW: 110571
