Fix #1170 Add "Don't Assign" option when configuring inputs

data/gui/press_a_key_dialog.stkgui

@@ -8,6 +8,8 @@
 
         <button id="assignEsc" I18N="When configuring input" text="Assign to ESC key" align="center"/>
         <spacer height="10" width="10" />
+        <button id="assignNone"    I18N="When configuring input" text="Assign nothing" align="center"/>
+        <spacer height="10" width="10" />
         <button id="cancel"    I18N="When configuring input" text="Press ESC to cancel" align="center"/>
 
     </div>

src/config/device_config.cpp

@@ -83,6 +83,10 @@ irr::core::stringw DeviceConfig::getMappingIdString (const PlayerAction action)
                 returnString += id;
                 break;
 
+            case Input::IT_NONE:
+                returnString += "none";
+                break;
+
             default:
                 assert(false);
                 returnString += type;

src/states_screens/dialogs/press_a_key_dialog.cpp

@@ -44,6 +44,12 @@ GUIEngine::EventPropagation PressAKeyDialog::processEvent(const std::string& eve
         dismiss();
         return GUIEngine::EVENT_BLOCK;
     }
+    else if (eventSource == "assignNone")
+    {
+        Input simulatedInput;
+        OptionsScreenInput2::getInstance()->gotSensedInput(simulatedInput);
+        return GUIEngine::EVENT_BLOCK;
+    }
     else if (eventSource == "assignEsc")
     {
         Input simulatedInput(Input::IT_KEYBOARD, 0 /* deviceID */, KEY_ESCAPE);

src/states_screens/options_screen_input2.cpp

@@ -447,6 +447,23 @@ void OptionsScreenInput2::gotSensedInput(const Input& sensed_input)
             updateInputButtons();
         }
     }
+    else if (sensed_input.m_type == Input::IT_NONE)
+    {
+        if (UserConfigParams::logMisc())
+        {
+            std::cout << "% Binding " << KartActionStrings[binding_to_set]
+                << " : setting to keyboard key NONE\n\n";
+        }
+
+        KeyboardConfig* keyboard = (KeyboardConfig*)m_config;
+        keyboard->setBinding(binding_to_set, Input::IT_NONE,
+                             sensed_input.m_button_id, Input::AD_NEUTRAL,
+                             Input::AR_HALF,
+                             sensed_input.m_character);
+
+        // refresh display
+        updateInputButtons();
+    }
     else
     {
         return;