Incorporate basic labs into j-playground

[joebo]

Labs are a great way to learn about J. Many of the labs have complex dependencies, such as plot, but not all of them. We can load simple labs into j-playground to give a taste of the experience.

Approach:

1. Find all labs that have no dependencies

joebo@LAPTOP-44R9IB1C:~/j-playground$ cat labs/build_labs.sh
#!/bin/sh
# simple script to copy labs into this folder that have a chance of working with j-playground
grep -r --include "*.ijt" -L "LABDEPENDS\|load" ../labs_labs/ | xargs cp -t .

2. Copy those labs into a labs folder under j-playground
3. Add a menu item to start each lab .Sidebar: it would be nice to preserve the folder structure, but we'll park that for now
4. Add a button to call labnext''