Various dependency clean-ups

Attempts to make the POM files a more accurate representation of what each module is actually using, and to standardise on placing versions in the root POM *only* (in the `dependencyManagement` section)

Testing: full unit test run; started Brooklyn and deployed MySQL+Tomcat cluster to localhost
What does this mean? Were we previously pulling in a transitive dependency of a different version? If so, do we need an `excludes`?