Expose some dom.js methods

[nickygerritsen]

This should fix #2683 by adding the four mentioned methods to videojs. I also added some simple tests that these methods exist and are correct aliases, but I'm not sure whether these should actually be in api.js?

[pam]

Tests failed. Automated cross-browser testing via Sauce Labs and Travis CI shows that the JavaScript changes in this pull request are: BUSTED

Commit: cfe5212
Build details: https://travis-ci.org/pam/video.js/builds/86340136

(Please note that this is a fully automated comment.)

[nickygerritsen]

....that Vista saucelabs thing...

[gkatsev]

Yeah, I'm trying to figure out why it's busted. Thanks for the PR.

[misteroneill]

Quick note. This looks good, but I have a very similar branch (rebased on my modal-dialog branch, which is why there's no PR yet) that does this and a bunch of other things like rewriting the *Class methods to use classList where available and improve tests.

[nickygerritsen]

Thanks @misteroneill I like your PR even more :)

[misteroneill]

I opened a PR for my branch: #2754

[gkatsev]

Closing in favor of #2754. Thanks @nickygerritsen for getting this started.