Add gcode buffer class with accompanying unit tests.
Change driver to use gcode buffer class.
Fix gcode cleanup. Fix progress message in command-line frontend.
Fix linecounting in gcode buffer (this also makes it prepared for streamed printing). Improve logging (ipc i/o is now logged as bulk).
Disable lowering max temperature check fails in marlindriver to avoid (wifibox-specific?) baudrate switches when printer moves to the center of printbed.