Add generic CSV export translator

For some tasks in my work with books I had to search for some literature and save some rudimentary bibliographic facts about each of them in a list (to work further). Moreover, I have read somewhere in the forum, that the "wish" for a CSV translator exists or take a look at http://belencruz.com/2014/03/how-to-export-from-zotero-to-excel/ or http://royce.kimmons.me/tutorials/zotero_to_excel . I think that nowadays it is more important to search and analyse larger parts of data easily, maybe also for bibliographic data. 

Here is a CSV export translator. The approach is to export all data, i.e. data fields from specific types are for the other rows empty. Moreover, the multiple fields and nested fields are translated as "paths" and can optionally also added appropriate.

Please let me know what you think.
to avoid issues with numbers, simply do `content = "" + content`

We should only need to escape the double quotes. Everything else should work as is (e.g. newlines inside quotes are ok). I see you do escape double quotes below, but I'm not sure if the same escaping works with other characters as wrappers. I would suggest to not make this variable (easily) configurable. The code is fairly clean and if someone needs to export in some non-standard format, I think they can easily figure out what to change and how to handle escaping.