Features/osx bundler

Creates `BaseX.app` using Oracles Application Bundler.
This is necessary for versions of Java not maintained by Apple (JDK > 6).

The ant build does the following:

* Uses http://maven.apache.org/ant-tasks/index.html to fetch version information from BaseX Core's POM
* Checks if basex-core has been built, i.e. the corresponding basex-$version.jar is available
* Bundles basex-$version.jar and ../basex-core/lib/*.jar
* Adds Retina Support to the application bundle (addOptions.xq)

To test run the following:

cd basex-core && mvn -DskipTests package; cd ..
cd app-bundle && ant && open dist/BaseX.app & cd ..