Merge pull request #1 from chicken-bone/cmd_startup

Added startup.py to engine

Adds Python 3 support.

Adds support for PySide2.

Updated for use with new core metrics

Clears qt lib paths for KDE Linux.

Removes Qt library path clearing.

Fixes crashes on multiple Linux distributions when QT_PLUGINS_PATH is…

… set.

Check for existing QApplication in engine.execute_command()

Allows context changes.

Engine is now less strict about when PySide/PyQt can be used to displ…

…ay UIs.