Do not set config defaults, if config says not to

so that we can include corporal as dependency to other projects
without the config interference

corporal/config.py

@@ -13,6 +13,9 @@ class CorporalConfig(ConfigExtension):
 
     def configure(self, config):
 
+        if config.getbool('rattail.config', 'corporal.set_defaults',
+                          usedb=False, default=True):
+
             # set some default config values
             config.setdefault('rattail', 'model', 'corporal.db.model')
             config.setdefault('rattail.mail', 'emails', 'corporal.emails')