Fixing flash autoplay so that loadstart is fired

The base media tech class now checks the networkState at init to determine if loadstart should be manually fired.

Previously this was only done in the HTML5 tech, but Flash needs it as well. This relies on videojs/video-js-swf#106.

Also removed the 'not implemented' warnings from the media tech functions. I think there's a better way we can help tech authors here, and it was blocking the ability to check if a function was implemented for real.

Fixes #1300, fixes #1341