Stonebox v2 - enclosure for your IoT Sensors

# Stonebox v2
This is improved version of my [Stonebox project](https://www.thingiverse.com/thing:3228067).

What I improved compared to original version:
* Thicker back cover which makes entire box stiffer
* Edges of back cover are now hidden, covered by side walls
* Back cover has a hole to hang it on the wall
* Improved screw holes used to screw back cover. Now they should print nicely without support

# Assembly
Glue the `front_lid.stl` to `side.stl` (I used ordinary CA glue), pack