Fixed bed plane equation
Removed inverse calculation (transpose == inverse)
Fixed the plane vector equation to a simpler one (only dependent on the normal)

Removed the calculation of the inverse matrix since the rotation matrix is orthogonal, therefore inverted == transposed.
Much simpler and mathematically robust.
Implemented a least squares fit of the bed equation for auto bed leveling.

The code for the LSQ solver (qr_solve) is copyrighted by John Burkardt and released under LGPL here:
http://people.sc.fsu.edu/~%20jburkardt/c_src/qr_solve/qr_solve.html
(see qr_solve.cpp for further copyright information)
Merge branch 'ozadr1an' of https://github.com/fsantini/solidoodle2-marlin into ozadr1an
Merging of the accurate bed leveling feature. If activated, the bed is probed in multiple points (default 4) and a linear least squares solution is taken for the bed equation

Conflicts:
	Marlin/Marlin_main.cpp
	Marlin/planner.cpp
	Marlin/vector_3.h
Enable Servo deactivation by default