Lichuan A4 servo in step dir mode

Lichuan A4 servo's, in step/dir mode, require a delay of at least 100 ms between the motor enable signal and the first step pulse. After stopping, depending on the tuning, they require time to completely stop the motor. Compiler option #define STEP_ENABLE_DELAY is added to config.h to enable a delay between the motor enable signal and the first step pulse. The delay (ms) is linked to grbl setting $1 that is already in use to delay the stepper disable signal after the last step pulse. This option is enabled by default!