Provide a pom.xml for maven users

this pull request tries to address issue #103

I had to update:
* suasync to 1.3.1 because 1.3.0 does not exist in maven central
* javassist version name because the version provided does not match the one provided in maven central (javassist-3.15.GA.jar to  javassist-3.15.0-GA.jar)

this only provides a way to compile src/test and gwt stuff using maven, this does not replace the full build process (gwt files linked in staticroot and dependency jar download to build/third_party for instance).

directory structure is not modified