Decongest CGroup for Variable creation and value setting

Partial testing and debug of XML read implementation to allow "< >" in
names. Required to allow STL containers as types (e.g.
"vector<double>").

Back to std::shared_ptr in CGroup members. std::make_pair calls the copy
constructor by default. Will keep track of std::shared_ptr counts.

Added more checks for debug version to guarantee exceptions.

To do: 
Add and test more types.
Add Capsule class and support.