OSGi class loading fixes

  * Changes the way bundles on the classpath are exported to felix - from list of exported packages in system.packages.extra to building extension bundles for each bundle on the classpath. This avoids the case where the same class would be loaded once from the classpath and once from a bundle referenced by a catalog item. When the catalog item tries to install the bundle we see that there is already an existing version installed and use it instead.
  * AggregateClassLoader doesn't relay to parent, using only the explicitly registered classloaders.
  * Force maven-bundle-plugin to include \*.impl.\* and \*.internal.\* packages in the export-package list (referenced between brooklyn bundles)

***NOTE***
Installing all the bundles in brooklyn-dist on my PC takes 3 seconds (once on startup). The slowdown is in Felix itself. Since we will be moving to OSGi based app we will need to load the bundles anyway so I don't see a way out of this.
Extension bundles are almost identical to the previous approach we used. Their goal is to direct Felix to use the app's classloader. The only difference is that now the container knows the name:version of the code that is on the classpath and will deny requests to install external bundles with matching name:version.
Felix still doesn't know for the existence of our bundle-A, we just tell it that the Export-Package list in the extension bundle should be looked for in the app's classpath. We don't ever install bundle-A in Felix. There is a hardcoded check that throws on an attempt to bundle.loadClass from extension bundle.

With that in mind, yes the code deliberately ignores extension bundles and goes directly for the app's classloader.