JENA-2343 - Bring back OSGi support to Jena

[laeubi]

Add OSGi headers to:

• jena-base
• jena-core

GitHub issue resolved #

Pull request Description:

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• [ ] Tests are included.
• [ ] Documentation change and updates are provided for the Apache Jena website
• [ ] Commits have been squashed to remove intermediate development commit messages.
• [x] Key commit messages start with the issue number (GH-xxxx or JENA-2343)

By submitting this pull request, I acknowledge that I am making a contribution to the Apache Software Foundation under the terms and conditions of the Contributor's Agreement.

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See the Apache Jena "Contributing" guide.