Enrich configuration files API to access to file names

Currently, when a configuration exception occurs (missing module, group, parameter…), it is hard to know what is the file where this information is missing.

We should add the possibility to access this information. Note that if several files are merged in one configuration, several files could contain the same information. Thus a kind of stack or list of files will have to be handled.

Also, the elements will have to be linked to their parents. What to do for inclusions ?

Start by tracing the configuration API and the exception paths for missing modules, groups, and parameters. Determine how merged configuration files and inclusions are represented, then define how source-file lists and parent links should be exposed. Done means the API identifies all relevant files and has documented inclusion behavior.

Written by the indexing model from the issue text.