Added thumbnails

Merge remote-tracking branch 'cover/thumbnails' into development

# Conflicts:
#	cps/admin.py
#	cps/templates/layout.html
#	cps/ub.py
#	cps/web.py
Update join for sqlalchemy 1.4

cps/__init__.py

@@ -96,7 +96,7 @@ def create_app():
         app.instance_path = app.instance_path.decode('utf-8')
 
     if os.environ.get('FLASK_DEBUG'):
-    	cache_buster.init_cache_busting(app)
+        cache_buster.init_cache_busting(app)
 
     log.info('Starting Calibre Web...')
     if sys.version_info < (3, 0):
@@ -121,6 +121,7 @@ def create_app():
 
     return app
 
+
 @babel.localeselector
 def get_locale():
     # if a user is logged in, use the locale from the user settings