add operator group for lookup (bug 894109)

A rough patch.

- Add an operators group which has permissions to use the lookup tool
- Adjust the lookup tool (https://marketplace.firefox.com/lookup/
) to only show App Lookup abilities to the operators group
- Adjust the Summary page (eg. https://marketplace.firefox.com/lookup/app/393011/summary ) to not show any of the Activity, Statistics, Edit Listing, Review History links to people in the operators group (unless that person is also the author or something, of course).