Merge adding theme support for audio and video

Hi,

I've been working on creating  a mobile application using DrupalGap. Thank you for building drupalgap. Its been very easy to bring up an application. I've needed to add these methods theme_video and theme_audio as I have embedded players in my application and felt that it would be useful for the community as well.

Could you please accept this patch?

Thanks in advance.

Cheers,
 -Vijay

@vjsamuel We should probably remove this static width attribute, and let variables.attributes handle it. We could set a default value for width if one isn't provided by the developer.