Improve validation on dashboard items field

rhodecode/model/forms.py

@@ -285,7 +285,7 b' def ApplicationVisualisationForm():'
 
         rhodecode_repository_fields = v.StringBoolean(if_missing=False)
         rhodecode_lightweight_journal = v.StringBoolean(if_missing=False)
-        rhodecode_dashboard_items = v.UnicodeString()
+        rhodecode_dashboard_items = v.Int(min=5, not_empty=True)
         rhodecode_show_version = v.StringBoolean(if_missing=False)
 
     return _ApplicationVisualisationForm