Turbo Everdrive Shell (updated for V2)

This is based upon the excellent Turbo Everdrive Shell by DogP. I've updated this to work on my v2.1 (I expect it'll work on other V2s as well, and would love for people to tell me what versions it works on) and made a few other changes.

**Changes from original 'no text label' version:**

* removed/rearranged some of the support structure under the surface of the shell to fit the V2
* added some more side wall structure where it was safe to do so to make up for the other change
* slightly