Connection recovery

Subscription is now able to withstand connection loss, it automagically resyncs after the connection to the server has been re-established. Private structures _modifiedItems and _sentItems are used to store the state of the subscription's events and ongoing requests, respectively.

DevOps reaction gif: http://devopsreactions.tumblr.com/post/78534868650/git-push-force

Motivating picture for branch merging: http://beargwills.files.wordpress.com/2011/12/lol-cat.jpeg