NGPC Flash Masta alternative shell

Simplified Flavor's shell design slightly to allow both the top and bottom of the shell to lay flat on the print bed. Less over hangs to deal with. Also note a new thumb notch was added to the lid to help with removing the cart from a NGPC system.

NOTE - Suggest adding printing support for the Base STL file. The Lid STL has support added directly to the model on one side. There's just a 0.2mm gap to help with removal.