* Add API to write error log * Move write_error api to system_log.write service call * Restore empty line
* system_log improvements * Don't use ModuleNotFoundError which is 3.6+ * Don't use FrameSummary which was added in 3.5 * Don't trace stack for exception logs * Handle test error in Python 3.4
Everything logged with "warning" or "error" is stored and exposed via the HTTP API, that can be used by the frontend.
