New Nord2000 calculation engine

Nord2000/Compro 2017: This update contains performance improvements as well as bug fixes. The bugfixes include correction of the Nord2000 sound propagation method as well as correction of the implementation. The corrections have mainly to do with how Nord2000 handles screens and how this was implemented, particularly in situations where the meteorology creates an acoustical “shadow zone”, i.e. in some situations when there is a wind component from the receiver to the sound source. The revised Nord2000 method report can be found here: http://assets.madebydelta.com/docs/share/Akustik/nord2000_nordtestproposal_rev4.pdf