* fixed fillSituationsArray to return correct initial situations
* VERIFY ranges and times to avoid inf/NaN and issues in general
* if invalid situations, continue with last situation
* count invalid situations
* flags for same parts/situation status
* transfer elevation (Ref T273) from previous situation
* preset elevation based on network situations if possible
* set elevation info
* function CInterpolator::initInterpolatedSituation
* using interface IInterpolant, renamed to CInterpolant for concrete implmentation
* CInterpolatorPBH has itws own file now, is included
* linear interpolator only re-calculates interpolant when needed (same as spline interpolator)