#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

ema/forms.py

@@ -80,7 +80,7 @@ class NewEmaForm(AbstractCompensationForm, CompensationResponsibleFormMixin):
             )
 
             # Add the creating user to the list of shared users
-            acc.share_with(user)
+            acc.share_with_user(user)
 
             # Add the log entry to the main objects log list
             acc.log.add(action)