Basic 18650 Case

I downloaded and printed many many 18650 cases, and decided to make one of my own, to address all the flaws that draw me crazy.

So here we go:

- This one does not need unnecessary thick walls, since it does not have a thread that requires fat walls

- I've made the chamber 19.1mm diameter, to accomodate some thicker protected cells, and also for ABS shrinking in mind, since I only print in ABS.

- It's sleek and linear design, perfect to fit the battery and just drop it in the bag, wit