More calendar fixes

* clarify non-shared message, also add for shared via calendar
* fix share dropdown being hidden and hiding calendar which will be shared
* remove confusing note, instead only make it possible to edit calendar sharing settings in the calendar settings cc @te-online
* only append (group) indicator to groups, no need to put (user) after every user
* improve look of sharing tab
* remove 'can delete' permission, also resolve CSS 'delete' class conflict cc @DeepDiver1975 @georgehrke 

Please review @georgehrke @owncloud/designers – Georg, I’m not sure if I did the removal of »can delete« correctly.