Fix memory leak for HeaderEntity instances:

the getArgumentCount() call in IfcEntityInstanceData destructor isn't virtually dispatched so it returns 0 instead of correct number of arguments => memory leak
added IfcEntityInstanceData::clearArguments() which clears all arguments and resets the attributes_ field to nullptr

Remove unnecessary copy in IfcEntityInstanceData::setArgument() when argument is created at the call site (no more leak of original argument)

Fix memory leak in IfcFile: delete entities from both byid and entity_file_map

src/ifcparse/IfcSpfHeader.h

@@ -36,6 +36,7 @@ private:
 	HeaderEntity& operator =(const HeaderEntity&); //N/A
 protected:
 	HeaderEntity(const char * const datatype, size_t size, IfcParse::IfcFile* file);
+	virtual ~HeaderEntity();
 
 	void setValue(unsigned int i, const std::string& s) {
 		IfcWrite::IfcWriteArgument* argument = new IfcWrite::IfcWriteArgument;