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.

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.

Follow-up the PR #3082
Follow-up the commit 143ad74: unnoticed updates
Fix for commit b0f5ba0: Z offset: -front [of the nozzle] +behind -> Y offset: -front [of the nozzle] +behind
Standardize the writing method: Z-probe, z-probe -> Z Probe
Adjust spacing

documentation/LCDLanguageFont.md moved to http://www.marlinfirmware.org/ at commit 12d0983757,
but http://www.marlinfirmware.org/ isn't working.

Enabling servo usage on boards with PWM current control
timer5 is used by some boards like the Mini Rambo for controlling motor current via PWM, see stepper.cpp.
```cpp
  #ifdef MOTOR_CURRENT_PWM_XY_PIN
    pinMode(MOTOR_CURRENT_PWM_XY_PIN, OUTPUT);
    pinMode(MOTOR_CURRENT_PWM_Z_PIN, OUTPUT);
    pinMode(MOTOR_CURRENT_PWM_E_PIN, OUTPUT);
    digipot_current(0, motor_current_setting[0]);
    digipot_current(1, motor_current_setting[1]);
    digipot_current(2, motor_current_setting[2]);
    //Set timer5 to 31khz so the PWM of the motor power is as constant as possible. (removes a buzzing noise)
    TCCR5B = (TCCR5B & ~(_BV(CS50) | _BV(CS51) | _BV(CS52))) | _BV(CS50);
  #endif
}
```
Using the same timer for controlling servos results in loss of motor control. So use timer4/3 for those boards instead.
[See discussion here.](http://shop.prusa3d.com/forum/software-f13/enabling-auto-leveling-in-firmware-t416-s40.html)

Thermister -> Thermistor

follow-up the commit b82d91eca6

SERIAL_ECHO is not very good in printing uint8_t - so cast. to int.

Add return to NOT_BUSY for M105
Replace WAIT_FOR_USER with PAUSED_FOR_USER

Add Travis test for FILAMENTCHANGEENABLE

Fix a SNAFU that should have been caught in #3012

The PrintrBoard Rev F utilizes a mcp4728 DAC to set motor current. Printrbot's implementation utilizes 2 new M-codes to set and write the DAC settings to the DAC EEPROM: `M909` (Read DAC) and `M910` (Write DAC). `M907` is re-used to set value, `M908` for direct control.

The Pins file for the RevF board is included.

Addressing #2773

Partial implementation with reference to MarlinFirmware/Marlin#3011

Alternative fix to #3149

Addressing issue #2767

Aim: Test probes in update_endstops only when activated

Changes:
Configurations
 Add define for FIX_MOUNTED_PROBE to handle the situation where formerly ENDSTOPS_ONLY_FOR_HOMING had to be set, or lowering the nozzle below Z_PROBE_OFFSET_FROM_EXTRUDER could give an "endstop hit" message.
 Add define for Z_MIN_PROBE_USES_Z_MIN_ENDSTOP_PIN to indicate a common situation, that we have a probe but it is connected to an endstop pin
 Add some comments
 Shift some entries to have related things together.

Conditionals.h
 We have a probe (HAS_Z_MIN_PROBE) if one of the pins is defined AND one of the probes is defined.

SanityCheck.h
 Add some tests if the probe is connected and if we have defined a probe.

stepper.cpp
 Changes to test the probe only when it is deployed (z_probe_is_active).
 Test update_endstops() when the probe is deployed.

MarlinMain.cpp
 a. set and reset z_probe_is_active in deploy_z_probe(), stow_z_probe() and dock_sled()
 b. set and reset z_probe_is_active in the case a z-servo is moved to a defined position. The only remaining unhandled servo move is in M280 where we do not end in a defined position. If you want to handle a probe use M401/402
 c. skip deploying/stowing when already deployed/stowed in the dedicated deploy/stow functions.
 d. Handle the new FIX_MOUNTED_PROBE in parallel to a servo driven probe/endstop.

 To do: In another PR. handle all probes in deploy/stow_z_probe.
 Sort out SERVO_LEVELING vs. HAS_SERVO_ENDSTOPS.

If Marlin is blocking the serial input or command queue for any length
of time (for example more than 2 seconds), it needs to send a message
to serial out to inform the host that it is busy. Marlin should only
send these messages out when busy, and preferably not when trying to
print formatted output.