Fix service mailman_meta

 - create new files also for empty mailinglists
 - slavescript can find differences between old state and new empty file
   state (even if all members are gone now)
Merge pull request #508 from stavamichal/fixMailman_meta

Fix service mailman_meta
add perun-engine-new and perun-dispatcher-new to the build, fix typo
Disable case sensitiveness for group names.