Merge mailetcontainer-library and mailetcontainer-camel

After thinking a bit more about the whole mailetcontainer-* modules I came to the conclusion that we should better merge mailetcontainer-library and mailetcontainer-camel. I think Stefano proposed exactly this before. I was against this change in the past but I think I now see the benefits.

At the moment we have mailetcontainer-library and mailetcontainer-camel which both use the same configuration file (mailetcontainer.xml). This is not really good as we need to ship the config file in both "bundles/modules".
I know the mailetcontainer-library has classes which don't depend on camel but as Stefano told before we can still split it later if we really need to..