Mongo directives

I created the ApplicationModel base class and got its tests passing.  TODOs:

1. There is still a warning about `safe` mode being deprecated in favor of :w => 1.  I don't know where this is coming from?
2. The Email `find_by_email` test is still failing (it was when I started).  The complaint is
```
undefined method `embeddable?' for nil:NilClass
```
I've been guessing that was the `user` association but I can't explain why that would be nil.