Avoid error when trying to send a selection of sql data.
Do not guess variable types for sql tables by default.
type_hints is an Orange domain.
Adapted tests for SqlTable guess_values.
Class value indexes should not be hardcoded as variables can be
recycled.
Constant time boolean evaluation of SqlTables.
Add option in Sql Table widget to enable domain guessing.
Refactor (cached) __len__ for SqlTables.
Normalize negative indices.
Paint Data widget refactor/rewrite.

Now using pyqtgraph instead of orangeqt.
Added some docstrings.
Group lines in parallel coordinates.
Use logger instead of prints.
Fix display of curves in parallel coordinates plot.