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.
added delta tower babystepping. Its untested, but hopefully florian horsch will be able to try.
also, removed some trouble for compilation with corexy.
I think that babystepping is only possible in z for a delta tower.
not sure if it would be usefull to step individual motors on a delta, i don't own one
Clarifying M280 command in Bed Auto Leveling section.