Set default MQ_HEADSIZE for Ultimaker
Significant refactor of planner

Simplify into just Region and Clearance classes.

Implement new improved algorithm.
Implement shift in lprng filter

Calls austerus-shift to generate new gcode.
Return to /var/spool/matterq but with queue subdirectory

Lprng is strict about its file permissions. The best option is to go back
to use e.g. /var/spool/matterq/lp or whatever the queue is called.

We still get multi printer support this way.
Refactor shifting in lprng filter and add test mode
Add lprng backend test

Allows testing of the whole planner system without a real lprng server
running. Arguments are the sequence of gcode files to print.
Add configuration parameter MQ_PLANNER_MODE

Defines how matterQ processes gcode.

none	Do not use planner
abort	Record depositions, abort if bed is not empty
shift	As above but shift print to available space on bed
pack	As above but shift even on clear bed for optimal packing
Implement planner modes in backend
Handle planner arguments for different modes and output commands in test