startkde: add new libexec tools to configure distro live sessions

this is a port of some neon specific scripts that mangle the live session so it doesn't fall apart due to baloo or lockscreens. I hope it's of use for others too

due to the nature of the beast this is fairly hard to test in practice so I've added some auto tests instead but I do fully expect some growing pains initially.

please note the README for how to use the two programs