Added multiple measurement support to projectQ backend

[QFer]

• Added additional multiple measurement support for projectQ
  • get_probabilities_multiple_measurement
  • unit tests for multiple_measurement
• Changed 2018 to 2022 in copyright notices
• Version updated to 2.0.0 because of major changes in result structures for the new api-version
• Added documentation for multiple measurement (api) (class docstring, get_result, get_raw_data_from_result)
• Changed description of measurement_mask in result structure in api.get_result docstring
• Added qi_results.py to readthedoc

[coveralls]

Coverage remained the same at 100.0% when pulling 62f2771da1cfc5930c401c3ff4ac5436a4af1fae on feature/sds-284-b/additional_multiple_measurement_projectq into a39f07a0e03681027005cf4a7ee81200fe20c265 on dev.