Updates to Enhance task

Allow Enhance to run auto with a configuration parameter (can be replicated by the user enforcing task dependencies in their build file), I'm not sure about this commit, comments would be nice?

The Plugin now uses the datanucleus enhance task directly, not the appengine wrapper which seems to be a little out of date??

It's easiest to use the v3.2+ of the enhancer
The user has to add datanucleus-jdo (optionally datanucleus-jpa) and datanucleus-core to the main dependency closure. Those include previously required datanucleus-enhancer and asm

The problem with this method is that dependencies that are only required for the enhancer now become part of the war :(, maybe we need a plugin for this or just stick to the appengine enhancer.