Modernize PartProp

• add 'final' qualifier when appropriate
• do not (explicitly) implement destructor if not needed
• do not explicitly disable default constructor which is not generated implicitly
• remove obsolete SVN/CVS keywords
• prefer std::unique_ptr over raw pointer and explicit delete
• prefer range-based for loops
• prefer auto for loop iterable
• prefer info(), error(), debug() over explicit MsgStream
• do not call default member constructors in constructors