added a button to invert page controls

reader/js/reader.js

@@ -172,6 +172,10 @@ document.getElementById("fitButton").addEventListener("click", function (e) {
     loadPage();
 });
 
+document.getElementById("invertButton").addEventListener("click", function (e) {
+    invertPage();
+});
+
 document.getElementById("titlebarContainer").addEventListener("mouseenter", function () {
     document.getElementById("titlebar").style.visibility = "visible";
 });

reader/reader.html

@@ -26,6 +26,9 @@
             <button class="titlebarButton" id="fitButton">
                 <img class="titlebarIcon" id="fitIcon" src="img/height.png"/>
             </button>
+            <button class="titlebarButton" id="invertButton">
+                <img class="titlebarIcon" id="invertIcon" src="img/invert.png"/>
+            </button>
         </div>
         </div>