add support for integrated database schema migrations

added the "initprovider" command to initialize the database structure.
If we change the database schema the required changes will be checked
at startup and automatically applyed.

dataprovider/sqlqueries.go

@@ -79,3 +79,11 @@ func getUpdateUserQuery() string {
 func getDeleteUserQuery() string {
 	return fmt.Sprintf(`DELETE FROM %v WHERE id = %v`, config.UsersTable, sqlPlaceholders[0])
 }
+
+func getDatabaseVersionQuery() string {
+	return "SELECT version from schema_version LIMIT 1"
+}
+
+func getUpdateDBVersionQuery() string {
+	return fmt.Sprintf(`UPDATE schema_version SET version=%v`, sqlPlaceholders[0])
+}