(for 2.7) Add support for setting `FormatFeature` via `ObjectReader`, `ObjectWriter`

With Jackson 2.6, `JsonParser`, `JsonGenerator` and `JsonFactory` support concept of `FormatFeature`.
But to try to keep some level of compatibility between adjacent minor versions, support at databind level needs to wait until 2.7. At that point, we should wire up things to allow setting these features, similar to general, non-dataformat-specific `JsonParser.Feature` and `JsonGenerator.Feature`.
