Persistent Mattermost alerts from the RCGUI

Now, the RCGUI sends alerts with custom message to a provided channel in Mattermost when one or more modules crashed or are in an error state.

To avoid missing them in the mattermost channel, the RCGUi also sends reminder alerts as long as the modules are not in a normal state. The time between reminders can be configured in the RCGUI configuration file (serverconfiguration.json).

Once a module returns to its normal state, a message (ok alert) is also sent to mattermost. The ok alert can be disabled in the serverconfiguration.json.