Reduced app binary size by optimizing bundled images.

Optimized bundled splash images (with "ImageOptim") to reduce their file size and also changed the way AspectThumbFetcher caches its image data so the bundled Pic of Day images could also be optimized to reduce file size. Commit b2203c5 includes optimized bundled Pic of Day images. Note: the change to the way AspectThumbFetcher caches image data should not affect usage of AspectThumbFetcher - it still returns the same data in the same way.