#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

user/admin.py

@@ -1,6 +1,6 @@
 from django.contrib import admin
 
-from user.models import UserNotification, UserActionLogEntry, User
+from user.models import UserNotification, UserActionLogEntry, User, Team
 
 
 class UserNotificationAdmin(admin.ModelAdmin):
@@ -64,7 +64,20 @@ class UserActionLogEntryAdmin(admin.ModelAdmin):
     ]
 
 
+class TeamAdmin(admin.ModelAdmin):
+    list_display = [
+        "name",
+        "description",
+        "admin",
+    ]
+    search_fields = [
+        "name",
+        "description",
+    ]
+
+
 admin.site.register(User, UserAdmin)
+admin.site.register(Team, TeamAdmin)
 
 # Outcommented for a cleaner admin backend on production
 #admin.site.register(UserNotification, UserNotificationAdmin)