updated database models [0.6.0]

This version introduces multiple enhancements:

created interface for resource
created empty class for multi table resource
modified resource abstract to return also object by first and last element

Details of additions/deletions below:
--------------------------------------------------------------

Added:      /Lib/Core/Db/Model/Resource/Multi/Abstract.php
            -- Added --
                empty class for multi table resource

Added:      /Lib/Core/Db/Model/Resource/Interface.php
            -- Added --
                interface for resource

Modified:   /Lib/Core/Db/Model/Resource/Abstract.php
            -- Added --
                interface
            -- Updated --
                returnRow to return also object
                returnLastItem to return also object
                returnFirstItem to return also object

Modified:   /Lib/Core/Db/etc/config.ini
            -- Modified --
                changed version from 0.5.0 to 0.6.0