RC Car battery strap post

Adapter to allow using battery straps in RC cars. Work in progress. Redesigned in Fusion 360 for CHAMFERRRRRS and eventually turned out in multiple versions - use as needed, remix as needed. Replace standard battery posts:  with these two printed parts and you can use a battery strap (more flexible and sturdy). Battery straps are "BangGood specials" - [4 USD for 10 straps](https://eu.banggood.com/10PCS-26cm-Eachine-Lipo-Battery-Tie-Down-Strap-p-1137622.html?p=AI10081335579201503X), very cheap and good [ESUN Yellow ABS](https://hobbyking.com/en_us/esun-3d-printer-filament-yellow-1-75mm-abs-1kg-roll.html?affiliate_code=NLVUDDBGDGZMRCT), battery is the (quite large) [Zippy 6000 mAh 2S2P 35C hardcase](https://hobbyking.com/en_us/zippy-6000mah-2s2p-35c-hardcase-pack.html?affiliate_code=NLVUDDBGDGZMRCT). The car is the always awesome [HPI Maverick Strada MT Brushless](https://www.hpiracing.com/en/kit/mv12623), also known as Redcat Volcano EPX Pro, HSP Brontosaurus, Exceed Infinitive, Himoto EMXT-1, Amewi Torche Pro (which are basically the same car). I've included all intermediary models in case somebody finds them useful. The final versions are: `BattHole_M26_shifted.stl` and `BattHook_M26_shifted.stl` which have an offset screw in order to fit properly into the chassis.