Work in progress: restoring broken functionality after a major database restructure.
The work is driven by the new unit tests in test/test_qt.py.
Implemented area select.
Z-order of items is generalised: no difference between types of items.
Fixed many shortcomings in the SVG export.
Added a 'bug' to the model, but no further support in the code.
Fixed many bugs.
Added support for PostgreSQL database repositories.
Added change logging.