made the widget movable

You can now move it to other bar.
An issue remain : when moved in new style mode the progress and image
texts are stuck. It works again if ff is restarted.
I also renamed a few ids/variables as to make more sense.
https://bugzilla.mozilla.org/show_bug.cgi?id=797841
There is an issue, firefox places the title centered under the whole thing but it's truncated so it's not visible.
Maybe there's a workaround I ll look into it.