Improve handling of 802.1x certificates

Certificates are now imported to $HOME/.kde/share/networkmanagement/certificates
for user scope connections and /usr/share/kde4/apps/networkmanagement/certificates
for system scope connections. This allows the user to move the original file out
of the way without worrying about connections. Certificates are passed to NM using
the path scheme to enable support for files containing multiple certificates.

BUG: 209673
REVIEW: 101275
(cherry-picked from commit c4932793)
had to some manual adaptations, should be fine (at least it compiles). Just revert
this commit if it doesn't work.