Prioritise directions with smallest head bounds for prints

By using these areas first we retain more printable space on the bed.
Add "pack" mode on planner

Shifts gcode by default even when there are no conflicts with existing
prints. This will result in the most efficient use of the print bed.
Change matterq-planner output format to include safe Z height
Pass safe Z height from planner through to austerus-shift
Add clearance to Z safe working height
Fix default setting of ZMIN
Refactor ZMIN handling