polybar: Get host width from bspc
polybar: Get host width from bspc

Although width can also be found through xrandr, it felt a bit messy to
parse output that wasn't meant to be parsed by other programs.

Since I can guarantee that the user will have bspwm (and not xrandr)
installed, I decided to use bspc instead. The current setup only works
for one monitor, but it should be relatively painless to setup multiple
monitors in the future (assuming they share the same dpi).

GloverDonovan/new-start