Single-screw TBeam case

Yet another case for your TTGO TBeam ESP32 LoRa board! I built this because I found the existing cases unsatisfying. The key features that I made sure to include are:

* Provides a single-screw closure, for easy access
* Securely holds your tbeam in place
* Provides button covers, to make it easy to operate all three buttons
* A comfortable shape to hold and operate
* Stands well on the bottom, back, or end, for antenna placement
* Screen is easy to read
* USB is still easily accessible
* Prints without support

I have a second variant of the design which is designed to accommodate the u.fl version of the board, with an SMA pigtail that mounts on the end. I find that an end-mounted antenna makes much more sense for my uses of the tbeam. These files are the ones with u.fl in the name.

In reconfiguring the design to make room for this change, I somewhat modified the main design -- I've re-exported the SMA STLs as well, which are slightly different than the