add db migrations

Author: lvaroqui

migrations/hiqlite/16_add_custom_email_mapping.sql

@@ -0,0 +1,4 @@
+ALTER TABLE clients
+    ADD cust_email_mapping TEXT
+        REFERENCES user_attr_config
+            ON UPDATE CASCADE ON DELETE CASCADE;

migrations/postgres/V11_add_custom_email_mapping.sql

@@ -0,0 +1,4 @@
+ALTER TABLE clients
+    ADD cust_email_mapping TEXT
+        REFERENCES user_attr_config
+        ON UPDATE ON DELETE CASCADE;