Intermediate push of experimental code for backup purposes

Nothing here is stable or fit for any purpose.
Intermediate commit of unfinished code for backup

Still not fit for any purpose.
Another backup commit of unfinished work.

Nothing to see here. Move on.
Another backup push ...

... still not functional but getting closer to something useful
Intermediate commit for backup purposes
Removed some outdated code
Intermediate commit for backup
Renamed some components; separate package for WDTK-to-DB conversion
Merge branch 'master' into db
Support for PropertyDocuments

* cleaned up code for interpreting ItemDocument to EdgeContainer
* fixed issue with domain sorts of qualifiers
Initial support for storing decimal values + minor improvements
Full support for Quantities
Initial code for recovering WDTK objects from the DB
Merge branch 'entity-baseiri' into db
Extened support for obtaining WDTK objects from DB objects
Extended support for storage backend, esp. decoding into WDTK

This is still preliminary code, committed mainly for backup purposes.
Merge branch 'master' into db
Use equals(), hashCode(), toString() and static constructors
Create objects for PropertyValuePairs when iterating edge containers

Reusing objects here is too dangerous and leads to errors.
Fix typo in methods for decoding statement rank