Changes to support devise-neo4j

I've been working to get the devise-neo4j gem working with the alpha version of neo4j.  I've done the work in the neo4j gem to make it support an orm_adapter, but when I ran the devise tests I hit a couple of snags which needed to be addressed in the devise gem.  They are:

 * Using adapters for User and Admin in the devise tests
 * Supporting both Time and DateTime model properties

Let me know if you have any questions about these changes!