Notification count fixes

Supports the new format for push notifications
Bump underscore to 1.7.0
Refactored UI activity aggregator

Attempt at simplifying the activity aggregator. Tests pending.
Ensuring activities with entities can be aggregated into activities without entities
Add  to the aggregation rules
Notification count follow-up

 * Aggregating folder-create and content-create on actor and target
 * Cleaned up JSDoc
Minor documentation follow up for UI push notification aggregation