Experimentation on rasters

I tried different things to make the scaling operation faster on my model of Raster.

Due to a bug in the treatment of `@inline` in Trait, I wasn't able to write code both fast and generic.

So now Raster uses a ByteColorModel, ie each ARGB component is written in separate adjacent Bytes.

I tried manually inline method but that doesn't really help the performances (decrease of 5% of the time needed for scaling), and was really ugly so I stepped back.

Here are my last results for the scaling benchmark (for 50 scaling):

    Testing Mortennobel Bicubic
    Time: 5891 ms
    Testing Mortennobel Bicubic in scala
    Time: 7291 ms

I think the timing is reasonnable enough to include this new version in the `master` branch.