Implement subscription history

[smallq-git]

In Frf there was a way to see your subscription history. This feature is useful for vanity and for memory.

Acceptance criteria:

1. In my subscription history I can see following events:
   • I subscribe to user/group (You subscribed to xx's feed/yy group)
   • I request subscription to user/group (You requested subscription to xx's feed/yy group)
   • I unsubscribe from someone (You unsubscribed from xx's feed/yy group).
   • I add user/group to a friends list (You added xx to zz)
2. Following information is available for all events: timestamp, username, action, friends list user belongs to.
3. Old data is browsable by pages (30 events per page).
4. Good to have data (wasn't present in Frf):
   • someone subscribes to me (xx subscribed to your feed)
   • someone unsubscribes from me (xx unsubscribed from your feed)
   • someone sends a subscription request (xx requested subscription to your feed)
   • I accept/reject someone's subscription (You accepted/rejected xx's subscription request)
   • I ban someone (You blocked xx)
   • I'm banned by someone (xx blocked you)

Page on Frf:

see Friends-2 spec, section Subscription History (russian-only): https://docs.google.com/document/d/1aJGR3v2O2a76U1lcDH9sJBZijeJRrdfjbh2f-pNoMLE