Refactor excerpt converter "contract"

Created by: wasabideveloper

Estimated duration: ~3d

• Move NAME, EXPORT_FORMATS and EXPORT_OPTIONS to an options file (one for each converter inside the module): Maybe we should use https://docs.python.org/3.4/library/configparser.html
• Remove module_converter_configuration function by a module property for each converter
• Create a test searching all converters and checking the "contract" -> existence of NAME, EXPORT_FORMATS, EXPORT_OPTIONS, converter_configuration, execute
• Document how to add a new converter