support for multilingual names using as:displayNameMap

elf Pavlikrequested to merge
github/fork/elf-pavlik/displayNameMap into master

modeled after http://www.w3.org/TR/activitystreams-core/#naturalLanguageValues

example in JSON-LD Playground of Group '(Taabir) تعبير' http://tinyurl.com/q8ptu7c

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