Add 'Follow file' checkbox in panel

Hi Nicolas,

I recently discovered your tool and it has really nice features.
Until now I was using BareTail.

I would like to contribute to add some cool features.
I am starting slowly and I would like to propose a checkbox in the toolbar in order to easily now if the file is followed or not.
I personally find it very useful.
Maybe I like this feature because I got some file update issues, like described here: https://groups.google.com/forum/#!topic/glogg-devel/kz08RQ7RmKE
So I am aware of what is the follow status without opening the menu.

Hope you are interested in this feature too.
(My future contributions will be discusses before starting some implementation ;) )

Regards,
Olivier