Server: fix the websocket api
SidebarApp: send a talkilla.sidebar-ready event to the worker
Refactor a lot of duplicated code in the worker tests
Worker: implement a tryPresenceSocket method

This method try to attach a websocket with the provided information, if it
fails, then it means the login expired.
Worker: try to attach a websocket when receiving the talkilla.sidebar-ready event
Worker: fix the tests
Worker: implement a _setUserProfile method
Worker: re-attach the websocket
SidebarApp: use a cookie for persistant login
Server: do not logout people that comes offline
SidebarApp: do not logout when leaving the page
Fix tests
Set an expiration time for the cookie
Server: allow users to be logged in but not present.
Worker: reuse _setupWebSocket
Fix jshint errors
SidebarApp: fix a duplicate event
Worker: document the talkilla.sidebar-ready event
SidebarApp: increase the cookie expire time
Addressing review comments