MKS SBase and Smoother Case for 2020 2040 Extrusion

This is a case for the MKS SBase (v1.3) controller that includes mounting locations for MKS Smoothers and an optional 120mm fan.

Notes:
* The MKS SBase is considered "[a cancer, a parasite](http://smoothieware.org/troubleshooting?s[]=mks#somebody-refused-to-help-me-because-my-board-is-a-mks-what-s-that-all-about)" by Smoothieware. You may want to consider supporting the project in some way if you purchase this board.

* Although it is possible to use external drivers, the SBase includes DR