tasks: rework the startTask API

it is now async. change was required to reset the pending flag

src/system.js

@@ -306,7 +306,7 @@ async function getInfo() {
 
 async function startUpdateDiskUsage() {
     const taskId = await tasks.add(tasks.TASK_UPDATE_DISK_USAGE, []);
-    tasks.startTask(taskId, {});
+    safe(tasks.startTask(taskId, {}), { debug }); // background
     return taskId;
 }