Stopwatch and PrintCounter improvements

PrintCounter classes

Additional instructions for controller reverse options

Extend M421 with I and J parameters

Extend M421 with I and J parameters

Update language_pl.h to the latest strings

MBL: Add option to configure G28 resting position for all axes

Buildroot cleanup

Moves Felix's dual configuration to a folder

Apply config changes, tweak comments, next_ping_ms => next_idle_ms

Rework intermediate idle() and manage_heater() calls in G2/G3 and G5

Update Galician language to 1.1.0-RCBugFix.

Remove SF_ARC_FIX from G5 (Cubic B-spline).
SF_ARC_FIX is a fix for G2/G3 (arcs) where Skeinforge always produced relative instead of absolute coordinates for the endpoint of an arc.
It's very unlikely this is also a problem with Cubic B-splines. More likely is copying from the G2/G3 code.

No compromises for the manage_heater(). manage_heater() will return immediately when there is nothing to do, but needs a constant detaT to work proper.
Calling idle() only every 200ms results in a display update every ~2 seconds - that should be enough.
For the other functionalities in idle() and manage_inactivity() 200ms is a lot but hopefully works.

Speedup sreen update delay
and correct a comment.

A module division by 10 is slooooow. (powers of 2 are fast - but then you can AND a bitmask with the same result)

Automatically set X2 stepper pins

Implements S1 argument in M999

DUAL_X_CARRIAGE fixes, improvements, Travis test

Update Japanese trasration

・Add new translation
・Change translation

Function declarations in headers don't need "extern"