Merge gcodeInterpreter optimizations from daid/Cura
Don't store layers or path points to save memory
Increase progress callback to every 1000 lines.

The processor handles 2500 lines per second on a 700MHz pi so as a baseline
that's still 2.5 updates per second.
Removed commented out and unused code
Merge branch 'CapnBry-gcodeinterpreter-upstream' into devel