Patch missing cols

[gaede]

BEGINRELEASENOTES

• add utility class CheckCollections that allows to parse lcio files for collections that are not present in every event and to patch such events with empty collections of the given (Name,Type) for further processing
• add example tool check_missing_cols that checks for collections that are not in every event in a set of files and prints a summary to stdout:
  • usage: check_missing_cols <input-file1> [[input-file2],...]
• add example tool patch_missing_cols that creates a copy of the input file with the same set of collections in all events:
  • usage: patch_missing_cols <input-file> <output-file>
• these tools are needed in cases where code expects consistent sets of collections in every event, as for example in a conversion to EDM4hep

ENDRELEASENOTES

[gaede]

Could we put the creation of the name to type map into a function and simply call that in check_missing_cols? That would make it much easier to use the same functionality in e.g. a standalone converter.

Yes, that's the plan - working on it ...