Refresh agent dashboard panel after create\update\delete operations (#1861)

* Edit alert WIP

* A couple alert edit bugs

* Hook up dashboard refresh notification

* Hook onchange event to other agent service calls

* Switch update handler to scalar value

* Add null check on handler callback

extensions/agent/src/test/testAgentService.ts

@@ -99,4 +99,7 @@ export class TestAgentService implements sqlops.AgentServicesProvider {
 	deleteJobSchedule(ownerUri: string, scheduleInfo: sqlops.AgentJobScheduleInfo): Thenable<sqlops.ResultStatus> {
 		return undefined;
 	}
+
+	registerOnUpdated(handler: () => any): void {
+	}
 }