#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

compensation/views/eco_account.py

@@ -796,7 +796,7 @@ def share_view(request: HttpRequest, id: str, token: str):
                 request,
                 _("{} has been shared with you").format(obj.identifier)
             )
-            obj.share_with(user)
+            obj.share_with_user(user)
         return redirect("compensation:acc:detail", id=id)
     else:
         messages.error(