Sequential Adapter for Simjack H Gear Shifter

### Sequential Shifter adapter for Simjack H Pattern Gear Shifter

Something came in the package to do similar, but it wasn't well measured so did not work well, so here's one that works better.

Key features:
* **Able to be installed WITHOUT removal of knob** unlike some that come with these Aliexpress shifters.
* **Tabs on the bottom**, which allow placing the adapter straight down into place, but prevent the adapter from lifting out of the slot when hitting the ends, especially as the switch levers sometimes get caught a little on the layer lines.
* **Stick stays centered with no pressure being placed to the left or right**, which in previous iterations caused binding against the gates. This is tested against the Simjack branded shifter only, I'm not certain the other very similar Aliexpress shifter models have the exact same positioning.