Raspberry Pi 3B octoprint mount with 3.5" screen and 40mm fan for 2020

Modified CSD_Salzburg's case for better cooling, added slot for Raspi camera cable. Also created a mount for 2020 extrusion with an integrated 40mm fan holder.

8/31/2017 Added hole for fan to back of sleeve, as well as more cooling holes, moved camera cable slot. Streamlined mount.