Code cleanup around MOTOR_CURRENT_PWM options

In all these cases we want the axis to be homed. If we could have lost
some steps is secondary.

Reenables homing seperate axis with DISABLE_X / DISABLE_Y true.

copy of 406992f9dd

Also add mbl.z_offset to the EEPROM, bumping the version to V23.

Fix a compiler warning in ultralcd.cpp

Closes #3235. Fix dogm lcd error when FAN_PIN is defined as -1

Further cleanup of comments, partial Doxygen-style

Following up on #3231

Fix spelling

Added GPLv3 header to all Marlin files

PROBABLE ->PROBEABLE
This is follow-up to #3069?

Toshiba Flash Air Wifi SD card support

Enabling servo usage on boards with PWM current control

Use arduino programming protocol by default for sanguino

Fix MELZI_MAKR3D to use correct motherboard

M120/M121 also set endstops non-homing state

Add Menu Items to initiate M303

Fixes for #3189

Setting a temp is still missing

Adds the parameter U to M303. If U1 is included , it will use the
PID-values from the auto-tune.

Follow-up the PR #3082, etc

Add support for Printrboard RevF

Make DISABLE_INACTIVE_X, etc., true if missing

Send position updates to RH

Patch minor spelling error in cn, en, gl language file headings

Fix lost undef Y_MAX_PIN in pins.h

Change link to the document

Fix Fan KICKSTART

Send position updates to RH where RH can not know the end position.

For example after G28 RepetierHost assumes to be at the homing-point,
but with a servo probe we are much higher. Now the RH-software-endstops
will prevent us from going down (if activated). With this patch the
internal position of RH is updated with `current_position[]`.

Sorting ot what else belongs to what if was not so hard.
But the static `ms = ms = millis();` was a bit surpising.

Patch-up to commits for Kana #3203.
Closes #3203.

Extend .gitignore

Improve Travis CI test