Log notification impressions and clicks
This logging was taken out by accident during the split notifications
Catrope mentioned this in rMW5ff1f9605e5d: Updated mediawiki/core Project: mediawiki/extensions/Echo….Oct 7 2015, 3:41 PM2015-10-07 15:41:32 (UTC+0)
Catrope mentioned this in rMW90cb21893be3: Updated mediawiki/core Project: mediawiki/extensions/Echo….
Catrope mentioned this in rECHO08293b2a417c: Follow-up f9e8c5057, 983c7a2463: fix JS error when there are no notifications.