ES6 Refactor

#####TODO

• Need a more advance way to extend objects instead of brut force merge.
• Track issue https://github.com/Dash-Industry-Forum/dash.js/issues/947 for new API needs.
• Add back in object name and media type for log system. (maybe throw error to get stack trace.)
• Make sure all var list are unchained when there is any assignment for consistency.
• Clean up the unit test helpers folder
• Make sure there are no unused imports in any class.
• DOCUMENTATION!!
• Get BOLA integrated
• Fix Internal Direct COST setting that is now not allowed. E.g. Look in DOMStorage how we are setting ABR const.
• Figure out where to put the dash create stuff now that there is not Dash.js file.
• Add API to set buffer pruning at MediaPlayer level. Can not directly assign to const value anymore. Make sure we expose all static const values that we may need access externally.
• Sort out unit test runner for mocha
• Add setInstance to add flexibility to Factory E.g Unit test
• Change Unit test folder structure to confirm to mocha test/unit.
• Inject Instance of Logger into all objects and stop passing as deps?
• Map all video element events to dispatch from mediaplayer instance.
• Restore/Fix Frag Abandonment
• Need ProtectionModel Detect system

#####Known Bugs

• Seeking back into Previous Period and them seeking or allowing the stream to playing back into next period fails.
• addBufferMetrics buffer target and virtual buffer level needs to be looked at.
• http://dash.edgesuite.net/dash264/TestCases/5b/1/manifest.mpd#s=80 MultiPeriod does not work in 1.5.1 or 2.0 if start time using fragment args is set.
• ended event not firing for MultiPeriod Content as of commit 28b1d2f 11/12/15 - this breaks the streamSwitch as it is not called from ended handler. Seeking into next period fires event to switch just fine.
• http://vm2.dashif.org/livesim-dev/periods_20/testpic_2s/Manifest.mpd Live MultiPeriod does not init and start properly.

#####Challenges, Changes, and Considerations

• Extensible code where needed. We can use the new extend method to override methods in any class or singleton like we did with context but even more useful as you can partial. But not true extensibility.

#####Build/Unit Tests

• ASAP stand up current test in new environment and add to test coverage.