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
why is it better not to do this?  i see you've included the version of these dependencies where they are declared as dependencies rather than recording these versions here, either should work, just curious why you prefer the new way...