PyXPad v0.6.0

Two new related features:

• Add ability to get available signals for a given shot (defaults to latest shot)
  • This adds a new source with only the signals available for that given shot. This source can still be used for other shots
• Add ability to filter a source by available signals in list of shots

The "last shot" button can now work without a source, assuming that UDA is available.

Plus some more minor changes:

• Adds lots of tests and general project tidying up
• Fix a few minor bugs:
  • When subtracting a constant, the constant was always 1
  • Fix right-division by scalar
  • Fix for descriptions printing empty dimensions
• Clean up UI a bit

Qt binding agnostic version

Uses Qt.py to wrap PyQt4, PyQt5, PySide and Pyside2 bindings for Qt4 and Qt5.