config: ensure the stage moves small step

also update the speed so that the time to wait for the move fit with the actual time it takes
mdupdater: ensure the correct MD_POS is observed

only a theoritical problem, as so far there is always just one stage
component: fix position reported for inverted axes

inverted axes were going the opposite direction... but the position reported was not inverted,
which was making the GUI crazy.
gui: change to official X/Y convention for world coordinates

We used to think that the world think like computer programmers. Apparently the world thinks that
Y goes up, so we need to inverse it.
Causes so problems in a few places which are not using the right conversion... still need to fix all the fall-outs.
comp: less debug messages

it would add 2 debug lines each time the spectrum or histogram is updated.
gui: clean up
gui: change A/B axes direction

Kind of due to axis convention better understood, and it just made things move the right way anyway.
gui: don't ask for stage move is the move is null

could happen when double clicking: a drag would initialise and immediately reset, with a 0,0 move.

Most of the drivers would discard the move eventually, but at least it avoids to receive too many
position updates.