Added install hooks to create empty dirs in /etc/udev

Something I found while browsing Makefile.am in systemd-udev, that
seemed like a good idea.
Merge branch 'libudev_to_rootlibdir' into axs
Merge branch 'remove_all_systemd' into axs
completed merge conflict, merge of hwdb_files_noinstall
Merge branch 'rule-generator' into axs