Refactoring and cleanup for pictures_controller
Re-enter the method for normalizing sizes

Without this method, cropping to a string greater than the actual image size will
actually blow the image up, which I guess is not what we want.

Plus, a ```#``` is used instead of a ```c``` for cropping as in my previous commit.
The ```#``` crops a (potentially very small region) out of a bigger image without
resizing it first.