#101 Team sharing form

* adds team sharing field to share form
* splits sharing logic into user based and teams based
* adds TeamAdmin for admin backend
* adds validity check on Team name -> only unused names shall be valid

intervention/forms/forms.py

@@ -253,7 +253,7 @@ class NewInterventionForm(BaseForm):
             intervention.log.add(action)
 
             # Add the performing user as the first user having access to the data
-            intervention.share_with(user)
+            intervention.share_with_user(user)
         return intervention