Make `CLDReconstruction.py` runnable from other directories

[Zehvogel]

At the moment one has to be in the CLDConfig/CLDConfig directory to be able to run the reconstruction. The main reasons for this are:

• py_utils.py are not installed into the python path (but maybe stuff from there that is still used should just be upstreamed anyway)
• The Pandora steering files are defined with a fixed relative path in the Pandora.py file (could be solved by asking __file__ where Pandora.py lives)
• All the sub files included by the sequence loader might need to be found (but maybe this already works?)

The goal would be to have a CLDReconstruction.py that can be run from the installed stack by just doing something like k4run $CLDCONFIG/CLDReconstruction.py