Incorporate improvements to our Maven usage

We want to make improvements to the way we're using Maven:

1. Start using the jboss-parent POM (see here for the source code on GitHub and the release notes)
2. The POM in 'modeshape-parent' should contain in the dependenciesManagement section an entry for all dependencies used in all modules, and the versions should be specified as property values. This makes it far easier to change/correct versions.
3. Create a parent POM for the sequencers by adding a 'sequencers/pom.xml' file, and move as much of the common declarations (including dependencies if that works) into this parent POM. Include the list of modules so that (a) we can build in the 'sequencers' directory, and (b) simply reference 'sequencers' as a module in the top-level POM.