Add engine setup parameter for non-Postgres DBs

Author: ndenny

example_config.ini

@@ -6,6 +6,7 @@ debug = True
 secret = a super secretive string
 
 [database]
+engine = postgresql
 username = grice
 password = grice
 host = localhost

grice/db_service.py

@@ -36,7 +36,7 @@ def init_database(db_config):
         msg = '"username", "password", "host", "port", and "database" are required fields of database config'
         raise ConfigurationError(msg)
 
-    eng_url = engine.url.URL('postgresql', **db_args)
+    eng_url = engine.url.URL(db_config.get('engine', 'postgresql'), **db_args)
 
     return create_engine(eng_url)