General refactoring

Fix: Refactor some bad blocks of code.
Add char return value support to DefaultChannelInvocation

Add: Interceptors that are generated by DefaultChannelInvocation support char return values.
Add boxed primitive return value support to DefaultChannelInvocation

Add: Interceptors that are generated by DefaultChannelInvocation support boxed primitive return values (e.g. Integer instead of int).
Add test for DefaultChannelInvocation generated return values

Add: A test for the generated return values of DefaultChannelInvocation.