Sort out maven builds

The maven setup has been refactored such that:

• Each module is built separately
• The parent POM is now in this distribution rather than an external project (as was the case in JBoss Cache)

What still needs to be done:

• distribution to be added as a module in the aggregator module
• mvn clean, mvn test (from root and from module directories) should not build javadocs unnecessarily
• mvn install should cause the aggregator module to:
• collate javadocs from all other modules in a single, coherent apidocs dir which can be uploaded to docs.jboss.org
• build distribution as a ZIP
• tests should work regardless of whether they are executed from within a module dir or in the root