Added support for partial responses in Youtube's URL title handler.

The handler now specifies what information is needed, which reduces
the traffic between bot and api.

Suggested by @lepinkainen in issues:
https://github.com/lepinkainen/pyfibot/issues/24
Merge pull request #68 from JaniL/youtubepartial

Added support for partial responses in Youtube's URL title handler.

Fixes #24