i3bar: Respect the urgency flag on status blocks

…by drawing urgent blocks with the same settings as an urgent workspace.

(Also use logical_px() and bar_height.)

fixes #682
use logical px
Merge remote-tracking branch 'origin/gaps' into gaps-next
Merge remote-tracking branch 'i3-original/next' into gaps-next

Conflicts:
	i3bar/src/xcb.c