mendel.c: Enable DEBUG_LED_PIN output if defined.
config.teensypp.h: Update to match testbed hardware.
heater.c: Limit PID I term with conditional integration.
heater.c: Enable more anti-windup with PID_CONDITIONAL_INTEGRATION.
heater.c, config.default.h: Make PID_CONDITIONAL_INTEGRATION non-optional.

See
https://github.com/Traumflug/Teacup_Firmware/issues/74#issuecomment-38999466