ScalaObjectMapper Wrapper

Every time I've used jackson module scala the first thing I do is create a simple util class that provides a subset of these features. So, I figured it was time to get this out there in a fully-featured way.

I would have really liked to handle both of these cases without code duplication:
```scala
val mapper = new ObjectMapper() with ScalaObjectMapper
```

```scala
val richMapper = new ScalaObjectMapper(providedMapper)
```

But the second option leaves you with an object mapper stripped of most of its functionality. Implicit conversions didn't work well since it's overloading an already existing function (my IDE seemed to understand what I was trying, but the compiler did not).

So you won't find the second option implemented in this pull request. If you have suggestions on how to provide both; I'd love to hear it.