Resolve "Validation of open enumerations does not search for @custom attribute"

[lukaspie]

Closes #666

Implementation is the following:

• Logic for closed enums remains untouched.
• For open enumerations where a value is used that does not match any of the enumeration items, the validator searches for @custom attribute (or @my_attribute_custom attribute for a a given attribute my_attribute).
• If that attribute is correctly set to True, we just give an info message.
• An warning level message is given if @custom is set to False.
• For HDF5 validation: If the @custom attribute is missing, a warning is logged.
• For template validation: If the @custom attribute is missing, we add it automatically to the template. As the produced file is then correct, we only log an info message (incl. the information that the attribute was added automatically).

Further changes:

• In the testing framework, I extended the logic for ignoring lines within specific sections in the log comparison. Now the person writing the test can just set ignore_sections = {"FIELD (//Ag__002__VB/start_time)": ["DEBUG - value:"]} and this will also ignore the "DEBUG - value:" line in all sections that start with "FIELD (//Ag__002__VB/start_time). We need this as for fields the line is actually DEBUG - ===== FIELD (//Ag__002__VB/start_time): <HDF5 dataset "start_time": shape (), type "|O"> and I don't want people having to give the whole line including the dataset information.

[RubelMozumder]

I left a few questions.

[RubelMozumder]

LGTM! I explained a unresolved comment further. You can take care of that if it makes sense to you.