make sure only admin can delete group in controller

is this what you mean @PragTob ? 
closes #206 

(i'm cleaning it up a bit thou first...)
it's probably my English that has gotten the better of me here (as I beleive I'm reading it as group's path) - however maybe saying group overview would be nicer - more in user terms than in programming terms (one of those high level style discussions, no real problem)