Added setting to keep / remove image metadata

We are using Caravaggio in some of our projects. Lately a customer of us received a notification that an image they're using does not have copyright metadata information.

We figured out, that the image metadata was removed during the image manipulation with Caravaggio. I added a configuration setting removeMetadata that allows us to configure whether the image metadata should be removed or not.

If you have any suggestions / questions about my merge request, please let me know.