Importer for the Citeulike JSON exporter format.

As we're increasing the number of formats to be imported, I've decided to create a new library to deal with them. The old imports are tied to PHP page code! =[

In this approach, the import functions uses the Getboo functions to add content. This is not the faster way to do it, but is the more general. As the idea is to crawl content and add them (in an incremental way), I don't think the speed will be a concern here.