Vapour transport

Merge the latest revision of vapour transport as authored by Mahdi Jafari.

Current state: Builds and tests pass.

Required changes still to be completed:

• Cleanup commented out/redundant lines
• Remove local references in Makefile
• Remove unnecessary build files
• Provide toggle of Vapour Transport at build time
• Provide toggle of Vapour Transport in runtime .ini
• Add Eigen as optional build dependency when Vapour Transport is not built