Make nimdowbar a separate program

[avahe-kellenberger]

trafficstars

It's been requested to use nimdow's bar in other window managers - separating it into its own program would be necessary for that to happen.

[avahe-kellenberger]

Some notes:

• We could support the typical workspace workflow most WMs have pretty easily, ootb
• Representing tags is not uniform between tag-based WMs. We would need to support the following data:
  • Which tags are selected
  • Window IDs mapped all respective tag numbers