Handle exceptions better - YouTube URLs that aren't to videos case an exception.

Currently, it is assumed that all links that have a domain of www.youtube.com are actually YouTube videos. Maybe be more sure before proceeding:

1. Check if there's is a key v in the query string.
2. Check if there is at least one value for that v key.
3. Make sure that video exists (eg handle cases where the thumbnail or get_video_info doesn't return an acceptable status code)