plugins.justintv/twitch: Updates for service changes.

- Remove RTMP streams since they are likely to be disabled soon.
- Remove mobile streams since they are the same as the new desktop streams.
plugins.justintv_common: Remove the legacy name option.

We don't get the resolution information anymore.
docs: Remove Twitch/Justin.tv specific rtmpdump issues.
plugins.twitch: Add support for OAuth2 authentication.
cli: Hide deprecated command line options.
plugins.twitch: Support VOD URLs with a time parameter.

This adds support for the ?t=00m0s URLs described here:
http://twitchtv.wordpress.com/2011/10/24/new-functionality-link-to-a-specific-time-in-a-vod/