Half-pad Start/Select button for dance pad

@rooood_75099 made a fantastic PIU pad. I however mainly play DDR style, but I like the option to play a full nine-arrows. I realised that the centre pad of rooood's PIU pad is very suitable for a nine button pad. Currently I use a cheap foam pad that constantly moves, unless you tape it in place. What I like about that pad, is that it fully controls the game. It has eleven buttons; nine arrows, and smaller start and select buttons to the left and right of the controller unit, which is top centre. For my hard pad I'm going to make a build that provides the full input functionality of my foam pad. To do so I needed smaller start and select buttons.

I'm a FreeCAD user and I couldn't open the original Fusion 360 files by rooood, as the current Fusion 360 has a bug that prevents it from starting on my system, and the FreeCAD import tool for Fusion360 files segfaults on this model. Therefore I directly modified the STL file in Blender and just eyeballed it.

I've tested the pad with the sensors and realise that it won't be as responsive as the gameplay pads. If you only press down on one of the sides, it won't register. You must properly depress the centre. However that's fine, as this is only used to control the game menus and doesn't need the responsiveness you need for gameplay.

I also made two LED holder remixes suitable for this pad (also eyeballed in Blender). I still have to evaluate those, but if it's sturdy enough, I'll go with the narrow design. It better aligns the LEDs with the shape of the pad.