Improve duplicate key handling

This issue tracks the implementation of duplicated key handling in JSON files used.

In normal situation, the files should be edited and stored using beat/beat.editor> or currently still beat/beat.web> however if one does edit the declaration file by hand, errors like duplicated key might be introduced which won't be caught as loading a JSON file line by line will result in a dictionary with the last entry being used (which is normal behavior when dealing with dictionary type of containers).

In our case, the system will generate an error so that nothing will run with unexpected values.