Mismatch between ignore_alerts in MW and UI

"ignore_alerts" used to be a single boolean value, but now you can ignore different types of alerts, so the UI sends a string array. The MW did not change between 2.0 and 2.1 to reflect this.

Example error seen on a 2.0 instance:

ERROR: servers/edit - Could not process args: {"id":"2kwvcgnowxvypch2","ignore_alerts":["warning","critical"]} . Error: json: cannot unmarshal array into Go struct field ServerObjectPublic.ignore_alerts of type bool