Generate patient charts with prawn for great justice

[Cart #45](https://trello.com/c/VRUDEXE6) in Trello

This should make it possible for us to skip a bunch of the [workstation setup](https://github.com/mission-of-mercy/mission-of-mercy/wiki/Workstation-Configuration) currently required when printing charts.

## TODO

- [x] Allow each workstation to specify which printer to use