ISIS-772: reimplemented.

... so that WrapperFactoryDefault now uses javassist.  WrapperFactoryCglib is the original impl.  To use, explicitly include cglib-nodep and asm in pom.xml (they are now marked as optional).

In addition:
- new tests in todo app to demonstrate some of the usage of this
- fixed an error that the use of 'modify' in wrapped methods was not being disallowed
- resurrected previously-@Ignore'd unit tests for wrapper factory.