Avoid exception on startup if Apache Tika is not available

If Apache Tika is not available, a long exception stacktrace is logged as the DS component can't be instantiated. This is due to the fact that the component is lazy (which is good) and therefore DS registers a ServiceFactory for it. The ServiceFactory eventually returns null which then must be logged by the framework. Therefore there is nothing we can do in DS to prevent this logging.
As this is a simple component with zero references, zero configuration, it is much better to register it via a BundleActivator if Tika is available