cubicweb #525245 devtools: have a default csv format compatible with import [deprecated]

We should have a clear text import/export format easily reusable.

For example in order to easily synchronize data between a demo instance and code repository.

See cubicweb/web/views/ to match the requirement of the input format defined in cubicweb/devtools/

Maybe a new csv input form view can be useful as well.

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