BBSHD Gasket Controller / Flat version

The [controller gasket seal by Tomblarom](https://www.thingiverse.com/thing:4560244/), does not mount on my BBSHD, so I redesign it to include the flat portion at opposite of data connector.

After quick full redraw of the model, I realized that the mold cast seems to be correct. So I could have simply done an intersection operation instead of this redraw. Anyway now it is done (and parametric)