Document groups

[Evildoor]

Currently, all documents are processed (for example, saved or exported) together. This is fine as long as there is only one corpus of documents, but when you have several corpora and need to gather statistics for them separately, you have to manually move "papers" and "export" folders around, or to deploy another instance of PDF Analyzer, or to do something else. Some kind of mechanism to group documents together and only process one group at a time will be of use to deal with such kind of situations.