Occasionally, I see complaints about the file organization of kwin,
which is fair enough.
This change makes the source code more relocatable by removing relative
paths from includes.
CMAKE_CURRENT_SOURCE_DIR was added to the interface include directories
of kwin library. This means that as long as you link against kwin target,
the real location of the source code of the library doesn't matter.
With autotests, things are not as convenient as with kwin target. Some
tests use cpp files from kwin core. If we move all source code in a src/
directory, they will need to be adjusted, but mostly only in build
scripts.
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.
