Upgrade Peewee to latest 3.x

This requires a number of small changes in the data model code, as well as additional testing.

tools/orphans.py

@@ -1,11 +1,11 @@
 from data.database import Image, ImageStorage
-from peewee import JOIN_LEFT_OUTER, fn
+from peewee import JOIN, fn
 from app import app
 
 orphaned = (ImageStorage
             .select()
             .where(ImageStorage.uploading == False)
-            .join(Image, JOIN_LEFT_OUTER)
+            .join(Image, JOIN.LEFT_OUTER)
             .group_by(ImageStorage)
             .having(fn.Count(Image.id) == 0))