Allow custom context for identity.SpecificName

[bb]

As proposed in ​phab:D2995, it would be useful the have custom contexts for identity opposite to the generic one possible by public/l10/messages.json. SpecificName template entries. The template schema, should be the same as in ​phab:D2995 (so an optional context attribute, an example schema is in attack.js, this should be ported to identity.js). Then one should process the context through the code: find all cases where the specificName is translated in the gui and process the context to that point.

A followup ticket/patch can use the attribute. A proposed usecase is the Greek words, where applicable.