add management command to remove the dashboard preferences

admin_tools/dashboard/management/commands/clear_dashboard_preferences.py

@@ -0,0 +1,8 @@
+from django.core.management import BaseCommand
+
+from admin_tools.dashboard.models import DashboardPreferences
+
+class Command(BaseCommand):
+    help = """Clears dashboard preferences."""
+    def handle(self, *args, **options):
+        DashboardPreferences._default_manager.all().delete()