Update tutorial for 0.3.5 + bugfixes and other improvements.
Formatting fixes.
Merge branch 'master' of https://github.com/Polymer/docs into tutorial-update-0.3.5

Conflicts:
	docs/start/tutorial/step-4.md
Merge pull request #616 from arthurevans/tutorial-update-0.3.5

Tutorial update 0.3.5