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
See https://github.com/apache/incubator-brooklyn/pull/99 - still required by some projects unfortunately.