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
Simply because a there were more intra-Brooklyn dependencies appearing so this list would have to grow. I thought it simpler to just declare a rule that *"intra-Brooklyn dependencies must always say `<version>${project.version}</version>` and external dependencies must only declare `<version>` in the root pom.xml."*

No strong opinion on this however, and my reasoning is not hugely compelling...