Added Turtle page 4 for Stage Algorithms.
Minor style change.
Fixed the free_play setting bug.
Merge remote-tracking branch 'origin/mooc' into fix-tangram

Conflicts:
	src/turtle/template.soy
	src/turtle/turtle.js
Added freePlay in the level config.

Conflicts:
	src/turtle/turtle.js
Remove dead code
Re-arrange some code to minimize diff between maze & karel