GBNG: new sakai.property to control visibility of 'Grade Entry' panel in 'Settings' UI

We had an institutional requirement to hide the 'Grade Entry' panel in GBNG's 'Settings' UI from non-admin users. We found that users were flipping these settings without realizing the consequences, which resulted in a lot of support calls.

We implemented this behaviour behind a new sakai.property (gradebook.settings.gradeEntry.showToNonAdmins) which defaults to true to preserve OOTB functionality.

For those who wish to hide this setting from end users, but still be able to make the changes with an admin account, simply set the property to false.