Implement proper support for GaudiConfig2 for the python components.
The basic idea is to dynamically (on `import`) change the base class of
of `CfgPyAlgorithm`, etc. Implement a trivial `merge` method that checks
if two instances are identical. More complicated merge logics would have
to be implemented in derived classes.

This also removes the need for special handling in the
`ComponentAccumulator`.