v1.15.0

Most important additions and changes relate to the following topics:

• Improved transparency of IAO import process.
• License related axioms have been generalized to account for other types of licenses besides copyright.
• General repository cleanup

A comprehensive list of additions, changes and deletions can be found at
https://github.com/OpenEnergyPlatform/ontology/blob/master/CHANGELOG.md#1150---2023-05-31