#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/admin.py

@@ -1,6 +1,7 @@
 from django.contrib import admin
 
-from user.models import UserNotification, UserActionLogEntry, User, Team
+from konova.admin import DeletableObjectMixinAdmin
+from user.models import User, Team
 
 
 class UserNotificationAdmin(admin.ModelAdmin):
@@ -64,10 +65,11 @@ class UserActionLogEntryAdmin(admin.ModelAdmin):
     ]
 
 
-class TeamAdmin(admin.ModelAdmin):
+class TeamAdmin(DeletableObjectMixinAdmin, admin.ModelAdmin):
     list_display = [
         "name",
         "description",
+        "deleted",
     ]
     search_fields = [
         "name",
@@ -78,6 +80,13 @@ class TeamAdmin(admin.ModelAdmin):
         "admins",
     ]
 
+    readonly_fields = [
+        "deleted"
+    ]
+
+    actions = [
+        "restore_deleted_data"
+    ]
 
 admin.site.register(User, UserAdmin)
 admin.site.register(Team, TeamAdmin)