Refactor for Job Queueing (incremental)

refactored 5DPrint.go heavily to clean up a few unnecessary channels as
well as reduce the number of background processes. Was able to put in a
proper job queue that should handle pausing better, but still a WIP

Added a Command struct to models, added a JobPaused field to Device and
included a few "error" constants to device.go
Refactor
Incremental

Pause / Resume working but need to optimize a bit more
Refactor attempt (unstable)
massive refactor and stubbing
cleaning of removed files
huge refactor and print queue logic rework
added missing files from previous commit