Allow for query parameter on has_many :videos

@claudiofullscreen Would love to get your thoughts.

I'm trying to replace youtube_it with YT, 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.
@stavro So probably we should have this:

    channel.videos # return all the videos in a channel. Can be your channel or someone else’s

    account.videos # return all the videos owned by the account

    account.videos(q: 'laser') # return all the videos owned by the account, filtered by laser

Would that work?