Alternative source to download raw images

[adrianmo]

Right now the Engine relies on the raw bucket and it needs a minimum amount of images to start building mosaics. If there are not enough images in the raw bucket, the Engine will fall into an active loop to check and download images until the threshold is met.

It should have a fallback mechanism when there are not enough images and download them from a known source. For example, it could download images from the following website: http://www.vision.caltech.edu/Image_Datasets/Caltech256/