Support liner notes with dockable slider (#1470)

* Support liner notes with dockable slider

- BRnavpos under BRnavMain is now hidden by default
- controlFor now accepts overrides for bookreader options
- Dockable slider forces display of page left/right controls

---------

Co-authored-by: IA Jim <jshelton@archive.org>

Author: pezvi

src/BookReader/Navbar/Navbar.js

@@ -33,8 +33,13 @@ export class Navbar {
     this.updateNavIndexThrottled = throttle(this.updateNavIndex.bind(this), 250, false);
   }
 
-  controlFor(controlName) {
-    const option = this.br.options.controls[controlName];
+  /**
+   * @param {string} controlName
+   * @param {Object} optionOverrides
+   */
+  controlFor(controlName, optionOverrides = null) {
+    const brOption = this.br.options.controls[controlName];
+    const option = Object.assign({},brOption, optionOverrides);
     if (!option.visible) { return ''; }
     if (option.template) {
       return `<li>${option.template(this.br)}</li>`;
@@ -273,8 +278,8 @@ export class Navbar {
                   <div class="BRnavline"></div>
                 </div>
               </li>
-              ${this.controlFor('bookLeft')}
-              ${this.controlFor('bookRight')}
+              ${this.controlFor('bookLeft', {visible: true})}
+              ${this.controlFor('bookRight', {visible: true})}
             </ul>
           </nav>
         </div>
@@ -286,7 +291,7 @@ export class Navbar {
                 <p>
                   <span class="BRcurrentpage"></span>
                 </p>
-                <div class="BRnavpos">
+                <div class="BRnavpos hide">
                   <div class="BRpager"></div>
                   <div class="BRnavline"></div>
                 </div>