Add command :status that shows a popup with sync info.

* Emit 'sync:conflict' on $rootScope when there is one.
* Let sync conflicts trigger a :status command execution.
* Make conflict event emitting mutable.
* Add mute button to popup.
* Show different sync messages when suitable.
* Toggle status popup on click on avatar.
* Update localTimestamp when localstorage changes.
* Set 'never' as default sync time.
* Indicate sync status on avatar