Support Free 2 part Mantis Tether

When tasked with making the Mantis Stand, the support requirement to print the original model upright was a bit daunting and wasteful. Separated the body from the base with a press fit groove, so the two parts can be printed support free.

Potental advantages of being packed away flater in a case, and also the base can be broken free in case of a snagging incident.