Add Marlin firmware. Has initial configuration for CoreXY and 1 servo.

Update CAD file with improved clearances for Pilot G2 cartridge clearances after first print.

Marlin Firmware/docker/Dockerfile

@@ -0,0 +1,7 @@
+FROM python:3.9.0-buster
+
+RUN pip install -U https://github.com/platformio/platformio-core/archive/develop.zip
+RUN platformio update
+# To get the test platforms
+RUN pip install PyYaml
+#ENV PATH /code/buildroot/bin/:/code/buildroot/tests/:${PATH}