Set the model attr when making new AppHandler object

or at least try, and ignore errors, which will likely happen if
e.g. the DB layer is not installed

rattail/app.py

@@ -66,6 +66,12 @@ class AppHandler(object):
     def __init__(self, config):
         self.config = config
 
+        # app may not use the db layer, but if so we set the model
+        try:
+            self.model = config.get_model()
+        except:
+            pass
+
     def get_title(self, default=None):
         return self.config.app_title(default=default)
 
@@ -79,7 +85,7 @@ class AppHandler(object):
         """
         import sqlalchemy as sa
 
-        model = self.config.get_model()
+        model = self.model
         return session.query(model.Store)\
                       .filter(sa.or_(
                           model.Store.archived == False,