Create a top-level parent pom that only contains dependencies/versions.

Currently it's difficult for a user to pull in the correct versions of dependencies used in the servicemix poms. It's possible to make one's project a child project of the servicemix parent pom, that gets all of the right dependencies in place but then brings in a lot of extra baggage such as maven build plugin settings that need to be overridden etc. It'd be handy for users if we could pull out our dependency management section into a top-level parent pom separate from the build plugin configuration, that way a user could make their project a child project and get the correct versions used in servicemix simply by pointing to the desired servicemix version.