Run qunit tests in default grunt task.

Use grunt-contrib-qunit to run the qunit tests with a headless browser.
Prereq to issue #24.
[Finishes #30]
Ignore node modules in git
Merge pull request #32 from ckundo/issue-30-add-qunit-task

Add task to run tests and run it by default
Merge branch 'master' into package-closure-library-35

Conflicts:
	package.json