v2.0.0

[MBueschelberger]

Since #49 was accidentally merged by a bot and has been reverted, this is the new pull request for milestone 2.0.0

• introduce new simplified mapping file schema
• introduce qudt and csvw for table annotation
• introduce pydantic into the package
• make method graph optional
• introduce new standard method graph using provo
• general package maintainance
• refactor modules
• add utility to read qudt-mapping from unit-symbols
• add utility to generate subgraph for quantity description using qudt
• support json files as input for mapping files
• drop unneeded intermediate file outputs
• update excel parser
• add json parser
• update documentation