Convert PdfSidebar to JS

ES 6 does not provide a direct equivalent for CoffeeScript's static
class properties so the initialization of `options` has been refactored
to use `Object.assign()` as a more idiomatic way to combine the config
args passed to the constructor with the defaults for `PdfSidebar`.

src/annotator/pdf-sidebar.coffee

-Sidebar = require('./sidebar')
-
-
-module.exports = class PdfSidebar extends Sidebar
-  options:
-    TextSelection: {}
-    PDF: {}
-    BucketBar:
-      container: '.annotator-frame'
-      scrollables: ['#viewerContainer']
-    Toolbar:
-      container: '.annotator-frame'

src/annotator/pdf-sidebar.js

+'use strict';
+
+const Sidebar = require('./sidebar');
+
+const DEFAULT_CONFIG = {
+  TextSelection: {},
+  PDF: {},
+  BucketBar: {
+    container: '.annotator-frame',
+    scrollables: ['#viewerContainer'],
+  },
+  Toolbar: {
+    container: '.annotator-frame',
+  },
+};
+
+class PdfSidebar extends Sidebar {
+  constructor(element, config) {
+    super(element, Object.assign({}, DEFAULT_CONFIG, config));
+  }
+}
+
+module.exports = PdfSidebar;