[#1280] Split save_thumbnail() out of save_image() method.
[#1280] Split save_thumbnail() out of save_image() method.

To allow thumbnail re-creation for example.

lym/allura-git,heiths/allura,apache/incubator-allura,heiths/allura,apache/allura,apache/incubator-allura,Bitergia/allura,lym/allura-git,leotrubach/sourceforge-allura,apache/allura,leotrubach/sourceforge-allura,heiths/allura,lym/allura-git,apache/allura,leotrubach/sourceforge-allura,lym/allura-git,Bitergia/allura,apache/incubator-allura,Bitergia/allura,leotrubach/sourceforge-allura,apache/allura,Bitergia/allura,heiths/allura,apache/allura,heiths/allura,apache/incubator-allura,Bitergia/allura,lym/allura-git