Add language

[jrmgx]

We may want to have different content for different languages (not sure yet)
If so, we are going to need a special parameter to specify/filter the language

This parameter could also be set as ALL for example and will show all the content available
the client could have an option so the final use can choose a lang not related to the client configuration (if he wants to learn a new lang)

I suggest we use the ISO 639 norm

Plan

• Add a way to specify the language filter
  I suggest something like ...?lang=[NORMALIZED_CODE|ex:en]
• Add an endpoint so we can list available lang
  including lang code, name and number of plays