Sphero Cardboard Maze Builder Improved

This design was inspired by Tzvih18's [Cardboard Maze builder](https://www.thingiverse.com/thing:3908761), but is ultimately a from scratch re-design. These were originally made to facilitate a STEM event that made extensive use of the [Sphero Mini robots](https://sphero.com/products/sphero-mini), and have been improved to work better with some other components included in the Mini Education Pack, specifically, the plastic obstacle sections and "wickets".

This version of the maze builder has also been designed to work with a base in order to make the mazes usable for larger numbers of children, and to support multi-level mazes to allow for obstacles that incorporate a vertical element of traversal.

Specific improvements include:
- Height increased to 1.25", about 3/4 the height of the Sphero mini
- Small protrusions have been added to the slots to improve the grip when using cardboard sections
- A widened area behind the protrusions for the ends of the "wickets" and obstacle sections