This allows the "label" callback to adjust the textbox itself.
`tasklist_label` is changed to make use of it and supports new style
arguments: `font_focus`, `font_urgent` and `font_minimized`.
Closes https://github.com/awesomeWM/awesome/pull/313.
Use `beautiful.xresources.apply_dpi` for `common.list_update`'s textbox
margins, and add a left margin for the imagebox, too.
The latter is useful/nicer with the default behavior of an inverted
style for the focused tasklist entry.
Uli Schlachter
Daniel Hahler
Julian Wollrath