Fixing iOS clipping, keyboard issues.

- Make sure that on iOS the clipping setting is always forced to be
  enabled.
- Hide the showKeyboard button unless connected.
- Use the URL text entry method and disable autocorrect and
  autocapitalize in the show keyboard input box.

vnc.html

@@ -70,7 +70,8 @@
                     id="showKeyboard" class="noVNC_status_button" 
                     value="Keyboard" title="Show Keyboard"
                     onclick="UI.showKeyboard()"/>
-                <input type="text"
+                <input type="url"
+                    autocapitalize="off" autocorrect="off"
                     id="keyboardinput" class="noVNC_status_button"
                     onKeyDown="onKeyDown(event);"/>
             </div>