Remove "run as root" feature

Decided that this feature should never have been added. It does not fit
in with the use cases targeted by this project. It is also not safe,
there are better ways to accomplish the goal of taking a backup of /etc
using kup.
Basically: if you are an advanced user, someone who backs up /etc, then
you can also set up an admin group, add yourself to that one and modify
files previously only readable by root to be readable by that group.
Or something like that.

bup was not written to be run as suid root.
Start using kdeinit for improved startup time

Resolves #2.
I noticed that there is no need to call "kshell4 kup-daemon" from the .desktop file's exec line. The kdeinit process will be asked to start it and if there's a library with the right name, that will be loaded instead of starting a new executable.