Since upgrading to Angular 1.6.1, selects with a default empty option
no longer show a popup with an error on submit. This fix adds an
empty option that is then removed with ng-if. Having the default
option set to null or undefined seems to be the cause of the bug.

The list of changes in 1.6 is here but could not find any obvious
cause for this bug:

https://docs.angularjs.org/guide/migration#migrating-from-1-5-to-1-6

Validate query to avoid self-reference of variable #7614

usermanagement: disable invite features when login form is disabled, cherry picked from master, #7875

Add reference to OpenID's userinfo_endpoint (as in #6351)

Also has the side effect of new panels having not collapsed queries when
being created

Typo fix for OpsGenie

Update alerting.md

fix: Data source group by time interval did not take effect on initial query after dashboard load, fixes #7839

Add missing `"`