Removed the argument type_str from get_default_prefix method on CollectContext.
The 'type' part of the prefix is now handled by the PathTemplate object.
Adding a facility to be able to handle some fixed parts of the prefix. These
fix parts are often related to the type of the collection, but can also
be used in other cases.

This is not the final solution to the problem but just a test solution.
Emitting a signal, mad_energy_selected, when a MAD energy is selected.
Using the PathTemplate object to handle the fixed part of the prefix
instead of CollectContext.
Using the EnergyScanResult of the crystal to pass store the result.