Fix typo in video tracks documentation

small typo
Merge pull request #1422 from SunnyLi/patch-1

Fix typo in video tracks documentation
add fix for localization of not supported message

add base documentation for language support

typo fix

added utility function for adding languages per conversation with @heff. Includes test.

move addLanguage to core. update both core and util tests. added export property

added language sandbox for demo

fix comment

doc udpate

remove build instructions

add addLanguage API to doc

fix deep merge in test

test update

update local reference to string for compiled tests
Added line to the changelog for #1427
Publish (i.e. prevent closure compiler from obfuscating name of) videojs.Player.prototype.selectSource function. This allows developers to provide their own algorithms for selecting which source a Player should use.
Added line to the changelog for #1424
Release 4.7.3
Merge branch 'stable'

Conflicts:
	dist/video-js/video-js.css
	dist/video-js/video-js.min.css
	dist/video-js/video.dev.js
	dist/video-js/video.js