Stackable Battery Holders Improved

This is a remix of all three stackable battery holders designed by [adoniram](https://www.thingiverse.com/thing:1004996) plus a new holder I designed for CR2032 coin-shaped batteries. The idea was to incorporate other ideas I found in various remixes maintaining the original design as much as possible.

I used the solution proposed by [7eggert](https://www.thingiverse.com/thing:3331733) which adds ramps on both the base and the cover that fix the jams as well as side holes that allow to see if there are still batteries left.

I also added the side borders to the end of the tongue to prevent the batteries from falling to the sides. Finally, I redesigned the way the cover is locked to the base at the bottom to facilitate the assembly. Based on my tests, the jam issue is now gone in all containers.

This printed very well in PLA as follows:
* cover - no supports, face down
* label - no supports, face down
* base - supports (80% overhang angle), back side down

__Update Mar 5, 2021:__ Added new improved cover and base extenders for models AAA, AA and C. They are based on the remix by [dlh567](https://www.thingiverse.com/thing:4784691). I added the side tabs and an extender for the C-format batteries. Also, cleaned up the thing files:
* removed different size versions for AA and C, leaving the slightly wider version
* made file naming more consistent

__Update Feb 10, 2021:__ A user fed back that when there were few batteries in the AA box they might jam at the…