Add possibility to mark translators in <titleStmt>

[lehkost]

Currently, we just accept authors in <titleStmt>, see here for an example. In this example (German translation of Shakespeare's Hamlet) we marked both author and translator as <author>.

We want to be able to mark translators as such, maybe using <editor type="translator"> (see TEI guidelines). <editor> is already allowed there, we would just have to allow the type attribute with value "translator".

After implementing that, we would have to address this change in the frontend (marking translators differently in comparison to authors, see the same Hamlet example rendered here).

In addition, we should a column (translator's name, if available) to the metadata tables.

[lb42]

Or you could use respStmt

[ingoboerner]

more generic see contributor role #71