First Version of DAI Zenon translator

Here is a first version of a DAI Zenon translator, which was adressed at  #769. It works pretty well with at the moment, but there are some issues:
 * It seems that all individual pages have the adress beginning with `http://zenon.dainst.org/#book`. But I have found books, bookSections, journalArticle among them. The `detectWeb` will in these cases always output `book`, which is sometimes wrong. This make also that the tests are not always working automatically. But the scrape function should output the right itemType with some nice metadata.
 * The `leader` and `controlfields` from marc are not yet imported, as I adapted the methods from MARCXML translator. I haven't found any function in the MARC translator for this. Is it possible?
 * The lines about bookSection and journalArticle involved a lot of guessing work, but it seems to work quite good.

I am not sure if MARC JSON is anyhow "standardized". The first few results from a google search, show different approaches (e.g. <a href="http://dilettantes.code4lib.org/blog/2010/09/a-proposal-to-serialize-marc-in-json/">here</a> and <a href="http://search.cpan.org/~cfouts/MARC-File-JSON-0.001/lib/MARC/File/JSON.pm">here</a>) to serialize MARC XML into JSON.
that's correct, but I don't think `.textContent` can be undefined. No big deal. You can clean it up if you want.