Improve OSGi metadata using Bnd.

The OSGi metadata has been improved, using the Bnd tool (http://www.aQute.biz/Code/Bnd) to generate it rather than maintaining a MANIFEST.MF file by hand.

Improvements include:

1. The exported packages are versioned. This is vital for consumers that need to target a specific version (or range of versions) of the API.
2. The required package javax.management is now explicitly imported.
3. The org.testng and org.testng.annotations packages are dependencies but have been marked as optional.
4. Thanks to Bnd, the dependencies specified in the manifest will always reflect the actual dependencies present in the code, as the code evolves.