Create a gallery of puzzle mechanics

[kostmo]

Let's create a new toplevel scenarios category (i.e. a sibling of "Fun"/"Tutorials", etc.) to serve as a collection of demonstrations of basic building blocks for more complex challenges. None of them need be fully-fleshed out scenarios with the obligation of polished maps and flavor text. In fact, the more bare-bones, the better, for the purpose of copy-pasting into larger scenarios.

Things that may belong in this category:

• demonstration of "trapdoor": #976
• portal demonstration (a la teleport.yaml/#406)
• minimal demo of enclosure checking (from #835)
• invent different types of enemies/dynamic obstacles

[xsebek]

Good idea, this would give some of our regression tests a higher purpose. :smile: