Copy / Clone method for handle and hgsetget class

Enable deep copying of child objects of classes handle or hgsetget

The handle or hgsetget classes miss a method to make deep copies of objects. The two classes "handleplus" and "hgsetgetplus" take care of this.

To use these classes, ...
- simply put them somewhere on your Matlab path.
- in classdef-files change instances of
"classdef MyClass < handle" (or hgsetget)
to
"classdef MyClass < handleplus" (or hgsetgetplus)

Suppose you have defined a "MyClass" as child of "handleplus". Deep copies are now created as follows:
>> OBJ = MyClass;
>> OBJ_new = OBJ.copy;

Some short notes:
- This implementation (hopefully) also handles deep copying of inherited private or protected properties (s. discussion "Clone Handle Object - using MATLAB OOP" -> link in acknowledgments).
- It handles properties, which contain handle-objects
- It does not handle cyclic references (s. mathforum.org/kb/message.jspa?messageID=7629086&tstart=0)

Please read the help for these files for more details and report any bugs.

Cheers

Sebastian