Allow for query parameter on has_many :videos

@claudiofullscreen Would love to get your thoughts.

I'm trying to replace youtube_it with YT on accounts, but currently the only missing piece is querying for videos.

This allows for the following usage (tested on my account):

```ruby
YT::Account.new(credentials).videos.map &:title
 => ["asdf",  "Vegas Indoor Skydiving", "Swing", "UCSD Dance by the Shores Adv. Hustle"]

YT::Account.new(credentials).videos(q: 'vegas').map &:title
=> ["Vegas Indoor Skydiving"]
```

Wanted to get your thoughts before i spend time fixing specs.
Ok.. I'll do that.

Btw, the `if @parent.auth == @auth` line would allow `channel.videos` to work on other people's channels (just not searching)... But yes, it should be more generic.  Ok.