Tulip 4.3.0

This is essentially a maintenance release with many bug fixes,
especially in the GUI, the OpenGL rendering engine and the Python Script view.

The GUI has been also updated with the redesign of:
- the Adjacency Matrix view's settings panel,
- the Node Link Diagram view's quick access bar,
- the Spreadsheet view's properties panel.

The Python Script documentation has been improved.

Finally some new features has been added:
- the NumericProperty class, a common interface to the DoubleProperty and IntegerProperty classes
(Most plugins which formerly accepted a DoubleProperty as input now accept also an IntegerProperty)
- 2 new rendering properties (viewLabelBorderColor, viewLabelBorderWidth),
- Qt5 support.