Set up to work with Maven

The XBRLAPI code base is now organised along the lines recommended for Maven projects. The code is organised into a variety of modules, each with its own project object model (pom.xml). The dependencies are clearly documented and minimised (eg: if you do not want to use eXist or Xindice as an underlying data store you do not need to use those modules). Overall, the changes should significantly improve the ease of setting up the XBRLAPI code base on your own system.