#229 Shared users mandatory on admin

* changes mandatory state of users and teams on admin backend to optional (as expected by the model)
* adds team selection to admin backend

ema/admin.py

@@ -6,12 +6,14 @@ from ema.models import Ema
 
 class EmaAdmin(AbstractCompensationAdmin):
     filter_horizontal = [
-        "users"
+        "users",
+        "teams",
     ]
 
     def get_fields(self, request, obj=None):
         return super().get_fields(request, obj) + [
-            "users"
+            "users",
+            "teams",
         ]
 
 admin.site.register(Ema, EmaAdmin)