Bed Auto Leveling feature

Check the Readme for instruction how to enable and configure the feature
Fixed duplicate define in fastio.h
Add the socalled "Babystepping" feature.
It is a realtime control over the head position via the LCD menu system that works _while_ printing.
Using it, one can e.g. tune the z-position in realtime, while printing the first layer.
Also, lost steps can be manually added/removed, but thats not the prime feature.
Stuff is placed into the Tune->Babystep *

It is not possible to have realtime control via gcode sending due to the buffering, so I did not include a gcode yet. However, it could be added, but it movements will not be realtime then.

Historically, a very similar thing was implemented for the "Kaamermaker" project, while Joris was babysitting his offspring, hence the name.

say goodby to fuddling around with the z-axis.
I think that filament change is ready for the masses. I have tested very often with my ultimaker.

I strongly vote for it being a single gcode, because otherwise the triggering from the menu is terrible.
merge from upstream