Add some IConverter instances for different data types
Modify SimpleConverter to convert arrays as well as objects
Add ObjectConverter, with tests

Also add a Priority property to IConverter. Turns out that we need this because
the order in which services are returned from StructureMap is nondeterministic.
ObjectConverter has to be returned last because it's a fallback in case none of
the other converters are available.
Model binding should be case insensitive by default