TH8 tactile feedback B1

We've all been there I guess; you create a nice design, print it and find out a couple small things could be better. I usually update the design straight away but I can't always be bothered with printing it again if it works good enough. Now, this is such a design:

* version B1: the original that I printed
* version B2: the improved version that I have not tested yet.

The improvements of B2 over B1 are:

* the spring plungers are positions slightly higher and closer to each other
* the top is rounded and lower on the front and back
* the tunnel for the tie-wrap is a bit bigger

I believe the B2 design is better, but like I said I have not tested it yet.

Both design try to combine the best features of all TH8A tactile mods that I know of:

* Use spring plungers to give resistance
* Fit nice on the axis and don't require another component to keep it down

**Update May 2020**
@rubenbeat printed the B2 version and confirmed that it worked perfectly. See hit comment a