Add:Tasks widget in appbar for merging m4bs & remove old m4b merge routes

server/managers/TaskManager.js

@@ -0,0 +1,20 @@
+class TaskManager {
+  constructor(emitter) {
+    this.emitter = emitter
+
+    this.tasks = []
+  }
+
+  addTask(task) {
+    this.tasks.push(task)
+    this.emitter('task_started', task.toJSON())
+  }
+
+  taskFinished(task) {
+    if (this.tasks.some(t => t.id === task.id)) {
+      this.tasks = this.tasks.filter(t => t !== task.id)
+      this.emitter('task_finished', task.toJSON())
+    }
+  }
+}
+module.exports = TaskManager