WIP authors: base record

* Defines fields and models for author base record.
* Adds new function for jsonalchemy models definitions.
* Includes tests for author base record.

There is one thing to add here: We need to store the list of the publications. This is a relaton between an author and a publication and this directly touches the subject of monday's meeting.
This function can be used for example for splitting `date` field into integers. Currently MARC format states that `date` of `100` field should be in form xxxx-xxxx (for example 1940-2009). In JSON we'd rather store those two values in separate fields.