[#156] ClassGroup.__repr__

I'm back on this and will elaborate a bit more:

1. Change the ClassGroup interface from
ClassGroup(label = "", props = None, group = None)
to
ClassGroup(props = None, label = "", group = None)

Rationale: The interface of ClassGroup differs from the interfaces of all
derived classes. The patch harmonizes the interfaces. Since
ClassGroup is only used as a base class the change affects only a
couple of files.

2. Change the ClassGroupProperties interface from
ClassGroupProperties(props)
to
ClassGroupProperties(lineColor = Black, lineWidth = 1,
size = 5, fill = Transparent)

Rationale:
In the current interface, props is a ClassGroupProperties object.
This recursion makes it impossible to implement a eval(repr())
for ClassGroupProperties, which are used by ClassGroup.

3. Change the __repr__ methods to realize eval(repr())
This should include more tests as your findings point out.

I propose to do the changes in three steps

Ping Frank.

Here is a testcase.
Frank, your patch fails the testcase, because
it does not output "ClassGroup" in front of the brackets.

Also: Are you sure that there are no other bad side effects in changing the ClassGroup interface? This seem to be two different things: a) making __repr__() output something reasonable and changing the constructor interface.

In personal communication Bernhard Herzog suggested that the repr in combination with eval() should again result in an instance of the same class.

I had to modify especially ClassGroupProperty, since the constructor expected an object and not the attributes representing it.

Please test the attached patch.

Frank