Bugfix, now uses correct pongTimeout
Invalidate timers on disconnect

Otherwise library tries to send a ping after disconnect, causing assertion to fail
Remove unnecessary pusher:ping event handling

This will never be sent by the server since the WebSocket draft in use supports native pings
Reset the pong timer on any activity

This simplifies the timer logic: It's no longer possible to have to a ping & a pong timer active at the same time.

Also consistent with the js client behaviour
Merge branch 'client_activity_timeout_fixes' into r1.5