#169 Team delete-restore

* adds restorable delete functionality to Team model
* refactors minor code model parts by introducing DeletableObjectMixin
* only non-deleted Teams can be chosen for sharing
* deleted Teams can be restored using the proper function on the backend admin
* deleted Teams do not provide
* adds migration

user/forms.py

@@ -230,8 +230,8 @@ class NewTeamModalForm(BaseModalForm):
             team = Team.objects.create(
                 name=self.cleaned_data.get("name", None),
                 description=self.cleaned_data.get("description", None),
-                admins__in=[self.user],
             )
+            team.admins.add(self.user)
             members = self.cleaned_data.get("members", User.objects.none())
             if self.user.id not in members:
                 members = members.union(
@@ -335,6 +335,10 @@ class RemoveTeamModalForm(RemoveModalForm):
         super().__init__(*args, **kwargs)
         self.form_caption = _("ATTENTION!\n\nRemoving the team means all members will lose their access to data, based on this team! \n\nAre you sure to remove this team?")
 
+    def save(self):
+        self.instance.mark_as_deleted(self.user)
+        return self.instance
+
 
 class LeaveTeamModalForm(RemoveModalForm):
     def __init__(self, *args, **kwargs):