Restrict link-sharing onboarding popup to admins.

Only people with admin permission to the Project can see the Share
button and dialog. It doesn't make sense to alert users who can't
interact with the feature anyway.

services/web/app/views/project/editor/editor.pug

@@ -111,7 +111,7 @@ div.full-size(
 
 #onboarding-linksharing.onboarding-linksharing.popover(
 	ng-controller="LinkSharingOnboardingController"
-	ng-if="onboarding.linkSharing == 'unseen'"
+	ng-if="permissions.admin && onboarding.linkSharing == 'unseen'"
 	ng-class="placement"
 )
 	.popover-inner