All CMake code that executes xsltproc is wrapped to functions that
ensure that arguments passed to xsltproc are all relative paths,
thus avoiding issues with spaces in the source/build dir parent
path containing spaces, which xsltproc on Windows just does not
like.

It also simplifies some of the CMake code and moves the
kcfg_generate_dbus_interface macro into KF5AkonadiMacros
so that we don't have to have a dedicated copies (that would all
need fixing) all over KDE PIM.

(Cherry-picked from couple of commits on master)