Add conventions for custom range and sort options

When registering a custom query value converter, I need a way to specify what the default sort option is, and whether the "_Range" fields are created.

I am working on a contrib project to add support for NodaTime to the raven client, and I need this for types like `Duration` and `Offset` which will mimic the functionality of `TimeSpan` in raven.  For example:

    documentStore.Conventions.RegisterQueryValueConverter<Duration>(CustomQueryValueConverters.DurationConverter, SortOptions.Long, true);