Converters

### REVIEW NEEDED ###

@dscho I tried to implement Normalizers and Converters in a clean way, especially such that we can optimize each and every op. Can you please review, comment, etc on the design. I'm aware of the fact that the commit messages aren't perfect, but I really wanted to see progress while I'm here and we really have to discuss design issues.

Anyway: We also need to figure out a way to auto-generated e.g. fast variants of GenericScaleIterableRT (ArrayImg/PlanarImg etc, for all the type combinations). We will see this pattern occur more frequently: Given one or two ArrayImgs of same or different type apply a pixel-wise function  on them. Maybe we can have a more generic way for creating such classes? any idea?