Implement GWT code generator

[sebhoss]

Currently the only thing that uses AOP and thus requires a framework that supports AOP is the ContractMethodInterceptor. It should be possible to switch this class for GWT projects. Instead of using AOP we could then generate the required Java code during compile-time and let GWT convert it into JavaScript for Browser execution.

[sebhoss]

References:

• http://www.gwtproject.org/doc/latest/DevGuideCodingBasicsDeferred.html#generators
• http://www.gwtproject.org/javadoc/latest/com/google/gwt/core/ext/Generator.html
• https://code.google.com/p/gwt-ent/