* Consolidate variant scripts
* Rename Marlin-local boards
* Simplify variants where possible
* Rename variants
* CHITU_F103 and MEEB_3DP: Maple platform `platformio-build-stm32f1.py` uses the 'board' name, not 'board_build.variant' so folder names match 'board' and not `board_build.variant`.
Implement initial support for MKS Robin (STM32F103ZET6) board.
Custom build script is used to generate encrypted firmware compatible with original MSK Robin bootloader (i.e. safe firmware update from SD card and possibility to go back to original close-source firmware).
