Core: Implemented property container.

        * src/core/Makefile.am: added new files to a build list
        * src/core/baseproperty.cpp:
        * src/core/baseproperty.h: single property wrapper implementation
        * src/core/propertycontainer.cpp:
        * src/core/propertycontainer.h: class containing all properties
          of a specified element/factory