Flash title when receiving lines in the background & make use of favico configurable

* Reflect the number of unread lines in the title bar
** This automatically flashes the title for a pinned tab in the background in Chrome, fixing #22
* Allow disabling use of favico

As mentioned in the commit message of https://github.com/lorenzhs/glowing-bear/commit/d4207ed7e0c481cf3d68f86d07e8e07dd79a08e8, we should discuss some points:
* Should the title reflect the number of unread lines or just notifications?
* Do we want to add this number to the title even if favico is enabled?