use of APIs (and API keys) should be optional

[adrienjoly]

After YouTube reduced Openwhyd's quota to their API, we realized that we were relying too much on Playem, which is also relying too much on YouTube's API.

This library should only care about embedding and playing content, not detecting and/or fetching metadata.

=> Proposal: move track detection and track metadata retrieval to a separate lib and/or to Openwhyd's bookmarklet, like we started to do in openwhyd/openwhyd#285.