Add Bosonic sample to the article 'Custom Element Interoperability'

As we cannot load the component via bower (we use only npm) I added the source within the commit. If you have another solution, please let me know.

Bosonic Elements are fully interoperable with Polymer, x-tags and vanilla, see http://bosonic.github.io/documentation.html#interoperability.

Let me know if I can help for something.

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Enguerran