Update travis CI file to test agains different databases, add travis DB setting files

mayan/settings/travis/db_postgresql.py

@@ -0,0 +1,11 @@
+from __future__ import absolute_import
+
+from .. import *
+
+DATABASES = {
+    'default': {
+        'ENGINE': 'django.db.backends.postgresql_psycopg2',
+        'NAME': 'mayan_edms',
+        'USER': 'postgres',
+    }
+}