Aurora release v23.03

Various build script improvements including:

• Builds the usd_view Python application which can be run directly from the build folder with the Aurora render delegate
• Added version detection to installExternals.py
• Refactoring externals folder layout
• Support multi-configuration builds with CMake
• Linux build fixes
• Security updates in externals versions

NOTE: Requires rebuilding the installed externals with the installExternals.py script as described in README.md