Resolve "noise widget fails (example_bm23.ows)"

Closes #54 (closed)

• fixed the noise task
• moved widget tests to est.tests
• fix a bug in the wait_task_executed method in the test suite
• the noise task allows the energy limits to be -1 (meaning min or max of the data range), do the same for the widget (the best would be for the widget to handle MISSING_DATA in some way)