Creates a "tools" extension module

Some modules like "referencing" contain utility classes with a main method. They are invoked from the command line in order to provide some information about Geotools configuration, like the screenshot attached to GEOT-1265. It may be worth to regroup the various main methods in a single "tools" extension module. Before to do so, it may be worth to list what current tools are, and how the tools module should be organized (package name, common option syntax, etc.).