Mixpanel - Tracking content downloads
Mixpanel - Segment searches into autosuggest, library and actual search events
Mixpanel - Track activity stream retrievals
Mixpanel - Library tracking

Added library tracking for:
 * content
 * discussions
 * folders
 * memberships
 * network
#1085 Follow-up

 * Alphabetized some event docs
 * Renamed mixpanel search events
 * Tracking activity transformer type
 * Tracking file download size
Mixpanel

 * One search event
 * Tracking user / group pictures
 * Cleanup