Homing fixes

- Prevent `Z_SAFE_HOMING` from homing Z twice in some cases
- Allow `G28` with XYZ values of 0 to explicitly set the position
- Don’t add `home_offset` when setting XYZ explicitly in `G28`
- Add `code_has_value` function to check for the presence of a numeric
value (could just test for space or nul to allow other types of values)

Fix doubled lcd_quick_feedback

- MENU_ITEM causes lcd_quick_feedback to be called, so only those calls
to `lcd_goto_menu` outside of the `MENU_ITEM` macro need to set the
`feedback` flag when calling `lcd_goto_menu`.

machine name for hephestos too

Apply CUSTOM_MACHINE_NAME to configs

- Replace “Mendel” with “RepRap”

Latest upstream commits

Break out prevent_dangerous_extrude feature

- In GCodes.md

- It’s inline here, but could be a macro and duplicated for
`planner.cpp`

Fix moves for DELTA for MANUAL_BED_LEVELING

Latest upstream commits

- Use `line_to_current` in place of `plan_buffer_line`

Made encoderPosition and quick_feedback dependant on NEWPANEL

Cold extrude

Z Probe inverting not present in example configs, causes error

where the hardware is available.
Fix for #1873

Latest upstream commits

Catch dangerous extrude before trying several

Added sanity check for MESH_NUM_X_POINTS and MESH_NUM_Y_POINTS

Moved the definitions of the LCD_STR_* to Conditionals.h

Latest upstream commits

Remove Contrast Menu for device U8GLIB_ST7920

The line const bool Z_PROBE_ENDSTOP_INVERTING = false; // set to true to
invert the logic of the endstop is in the main configuration.h but
wasn't present in the example configuration.h's. Causes a compiling
error with Z Probe enabled. Just added it to all the configs. :)

Resolved some warnings in Marlin_main.cpp regarding compares of signed and unsigned integers by replacing 'int' or 'uint16_t' with 'uint8_t'.

to avoid errors in Marlin_main.cpp. #1860

In the include tree of Marlin_main.cpp the decision between the display types is not made.
To include the right LCD_STR_* ether 'dogm_lcd_implementation.h' or 'ultralcd_implementation_hitachi_HD44780.h' with all their code.
A 'dogm_lcd_implementation.h.h' would be a curiosity.
So i moved both of the definition blocks to conditionals.h

On the long term it could make sense to use the same numbering for the u8glib and the hitachi symbols.

and cleaned typo.