Fix xdg-mime for proper Plasma 5 support
I realized xdg-mime does not run kbuildsycoca5 when fiddling with my defaults causing Plasma 5 to use old defaults.
This adds checks for Plasma 5 and runs kbuildsycoca5 after
updating mimeapps.list file. The path of the file is
I've tested it with empty mimeapps.list and
env var set.