[BUG] Move meta model elements from unit: to bamm: namespace

[atextor]

Describe the bug
Meta model elements are defined in the bamm namespace, the Characteristics catalog in the bamm-c namespace and the unit catalog in the unit catalog. One inconsistency is the definition of the meta model elements Unit and QuantityKind and their corresponding attributes, which are currently all defined in the unit namespace as well. To fix this, they should be moved accordingly.

Where

• Remove definitions from units.ttl
• Add definitions in aspect-meta-model-definitions.ttl
• Adjust textual descriptions in the textual units description

[atextor]

These changes should also be reflected in the changelog.