version 0.4.0 release

version 0.4.0 - 20200630

• Added gui and guiserver
  • a Qt-based node editor graphical user interface for Galaxy workflows
  • added nodeeditor submodule
  • added Qt5 dependency
• Added insitu socket connectivity for in situ workflows
• Added tracer streamline generation and rendering
• Added sampler methods
  • Gradient-based sampling
  • Isovalue-based sampling
• Added demonstration codes for new features in apps
• Updated to python3
  • python scripts
  • travis-ci config
  • travis-ci VTK-8.1 build