IP Scaling functionality far from optimal

Created by: anjos

The documentation and workflow of bob.ip.scale and bob.ip.scale_as as pretty bad as they currently stand.

1. If I read the doc of scale_as, I get the impression it will scale the input image, but actually it just generates a container for one.

2. The doc of scale does not precise the types of inputs it can handle, nor the type it outputs.

3. There is no easy handle to scale an image and return a freshly allocated container. I currently have to pass through scale_as to get a container and then be able to call scale.