basic video playback support using VideoJS

This update will make videos attached to a post display in a video player, while keeping the icon to download the video. The player will use HTML5 if the browser can play the video type, otherwise it will fall back to Flash. The Flash player can only play MP4s using h264 video and AAC audio. For HTML5, it depends on the browser and platform.

There's also a Videos page on the user profile to display all uploaded videos.