Added default support to DummyValueCreationSession for type Lazy<T>

Based off of the behavior that is defined for Task. Discussed in issue #358.
I see what you're saying. A few things to consider:

1. You just made up `IFoo` for the test, and there are no implementations. If you get an `IFoo`-like thing back, it _has_ to be something that FakeItEasy made up.
2. Yeah, if you do want to switch to a Dummy, you can just make a class that implements `DummyDefiniton<T>`. Then any Dummy created for `T` would come from that class, and so your new code would make any `Lazy<T>` use that. I think this is a very good way to go, as it shows that the Lazy really holds another Dummy, and it respects the dummy definitions that users may add.

Thanks for your patience!