Add in people properties to track last time users performed key actions

Added in people properties to track the last time users performed the following key actions:
* Last Time Accessed Reader
* Last Time Accessed Theme Browser
* Last Time Liked Article
* Last Time Reblogged Article
* Last Time Loaded Freshly Pressed
* Last Time Commented on an Article
* Last Time Stats Accessed
* Last Time Published Post
* Last Time Notifications Accessed
* Last Time Shared item

Fixes #1585