Imported the QUDT ontology for standardized measurement units.

removed s4mari:MaritimeProperty class and added s4mari:MaritimeObjectProperty for continuity between structures of saref subclasses

made s4mari:Metadata, s4mari:UniqueIdentifier and s4mari:Period all subclasses of saref:FeatureOfInterest

added s4mari:MaritimeObjectProperty class for coherence with subclass organisation of other saref core classes

added s4mari classes to ensure continuity in hierarchy between subclasses of saref:FeatureOfInterest and saref:FeatureKind and saref:State

added s4mari:EventProperty class to ensure continuity in hierarchy between subclasses of saref:FeatureOfInterest and saref:Property

added s4mari:EventKind and s4mari:AgentKind classes to ensure continuity in hierarchy between subclasses of saref:FeatureOfInterest and saref:FeatureKind

added links to corresponding CISE classes in CISE Core Vocabulary Specification for s4mari classes via rdfs:seeAlso

created s4mari class hierarchy diagram and seperate class hierarchy diagrams for Property, FeatureKind and FeatureOfInterest