WFCORE-14 - add operations for manipulating list & map attributes

initial version, i want do do some more cleanup of apis for easier manipulating on side of write/read attribute handlers
Just thinking out loud here, should we add a debug or trace log if the value was previously defined and is being replaced? Something like `debugf("Value '%s' for key '%s' being replaced by value '%s'., oldValue, key, value);`.