Allow to pause/stop the monitoring

Summary

In its current state, the monitoring application runs all the time if loaded and cannot be disabled. Since monitoring is known to cause issues in other sub-systems, it could very well create some in GEM. Some conflict cases are already envisioned.

Therefore a way to pause/stop the monitoring should be provided. Considering that the targeted hardware lease/lock granularity is per back-end board, the monitoring pausing should have a per back-end board granularity as well.

What is the expected correct behavior?

A system to pause/stop the monitoring for each back-end board should be provided.

As a first step, one or two buttons in the web interface can be enough. The control system should, however, rapidly evolve to a more complete remote API, such as SOAP or JSON.