Implement proper submission/solution comparisons.

This adds verification to all of the existing exercises.

Two new npm packages were created for this:

* gl-reset resets the state and clears up resources between
  renders.
* fresh-require allows us to bypass browserify's require cache,
  which prevents running the test from breaking the preview (which
	was caused by the value of top-level variables changing).

Also includes the workshop/compare package which compares two
init/draw pairs, and workshop/server-basic which eliminates the
need for boilerplate in most exercises' server.js files.
remove sample exercise
move over one more exercise to server-basic which I missed
IIFE analytics.js to avoid acorn parse complaints
Make overriding/wrapping the draw/init calls more convenient.

/cc @mikoalysenko
Merge branch 'compare-renders' of github.com:stackgl/webgl-workshop

Conflicts:
	package.json
Update texture lessons. Closes #21