Allow adding songs to multiple playlists at once. (#995)

* Add support for multiple playlists

* Fix lint

* Remove console log comment

* Disable 'check' when loading

* Fix lint

* reset playlists on closeAddToPlaylist

* new playlist: accomodate string type on enter

* Fix lint

* multiple new playlists are added correctly

* use makestyle()

* Add tests

* Fix lint

ui/src/setupTests.js

@@ -3,3 +3,18 @@
 // expect(element).toHaveTextContent(/react/i)
 // learn more: https://github.com/testing-library/jest-dom
 import '@testing-library/jest-dom/extend-expect'
+
+class LocalStorageMock {
+  constructor() {
+    this.store = {}
+  }
+  getItem(key) {
+    return this.store[key] || null
+  }
+  setItem(key, value) {
+    this.store[key] = String(value)
+  }
+}
+
+global.localStorage = new LocalStorageMock()
+localStorage.setItem('username', 'admin')