dist/{media,css,js} with {$APP,vendor}.js & more

- Cleaned out some unused files from static
- Created express.js dev server
- Converted html files to templates
- appMain function for common logic between Maze & Turtle
- loadLevel in Maze & similar in Turtle (slowly making them reentrant)
- Removed prettify.js (wasn't used in Maze, was needlessly lazy-loaded;
  can be re-added more generally and easily with smaller file size as
  highlight.js)
Eliminate static readonly.html

Readonly blocks are now injected in to an IFrame via JavaScript.
Commonize some strings