Add class (Application) to contain more details on AI applications

[caufieldjh]

This pull request introduces a new Application class to the standards schema, enabling entities to explicitly document their specific applications, especially those relevant to artificial intelligence in the Bridge2AI context. It also adds support for linking datasheets and references to applications, and updates the schema to include the new has_application field across multiple entity types.

Schema enhancements for application tracking:

• Added a new Application class, including fields for datasheets, references, contributors, and relationships to other entities. This class is designed to capture detailed information about AI-driven or other specific applications. [1] [2]
• Introduced the has_application slot/property to several entity definitions, allowing them to reference one or more Application objects.
• Added new slots/properties for datasheet and references to the schema, enabling applications to link to related datasheets and publications. [1] [2]

Schema cleanup and maintenance:

• Removed the has_ai_application slot from the schema, consolidating application tracking under the new Application class and has_application property.

These changes make the schema more expressive for documenting how standards, datasets, and other resources are applied, especially in AI-related contexts.