Nodegraphqt

- added port snapping falloff range set from `NodeGraphQt.constants.PORT_FALLOFF`
- global port size is now set from `NodeGraphQt.constantsPORT_DEFAULT_SIZE`
- updated live pipe draw Z order, the live pipe now renders above node and port items.
- refactored ``NodeItem`` port arrangement and layout functions.

- addressed issue 112

- updated `Qt.py` module to`1.2.0`
- implemented connection pipe slicer tool

- misconfiguration fix from ray-barrett
- minor updates to docs.

- added node properties bin widget.
- added node tree widget.
- updated sphinx docs.
- implemented ``set_text()`` function for BackdropNode.
- port type indicators.