Add back button to keys scene and allow fullscreen

Closes #29

webdata/fn.js

@@ -488,6 +488,11 @@ window.addEventListener("load", function() {
     document.getElementById("reloadbutton").addEventListener("click", function() {
         location.reload();
     });
+    document.querySelectorAll(".backbutton").forEach(function(button) {
+        button.addEventListener("click", function() {
+            history.back();
+        });
+    });
     document.addEventListener("touchstart", handleStart);
     document.addEventListener("touchend", handleEnd);
     document.addEventListener("touchcancel", handleEnd);

webdata/index.html

@@ -30,7 +30,7 @@
         <button id="sendbutton">➣</button>
     </div>
 </div>
-<div id="keys" class="touchpad key hidden">
+<div id="keys" class="touchpad key fullscreen hidden">
     <div class="page">
         <div class="buttons">
             <button id="browserbackbutton">⭠</button>
@@ -66,4 +66,5 @@
         </div>
     </div>
     <button id="switchbutton">⮂</button>
+    <button class="backbutton">⯇</button>
 </div>

webdata/main.css

@@ -180,6 +180,13 @@ textarea {
     border-right: none;
 }
 
+#keys .backbutton {
+    left: 0;
+    top: 0;
+    border-top: none;
+    border-left: none;
+}
+
 #keys .buttons {
     display: flex;
     justify-content: center;