overlay: "reset all" buttons for buttons/overlay/analog tabs (#578)

## Link to GitHub Issue or related Pull Request, if one exists
#576 

## Description of change
Add `Reset All` buttons to these tabs which clears out bindings to none
/ default.

For keypads, introduce a special `Use Preset` button which lets users
pick between numpad and top row number keys.

Update UI-visible string used for vKeys, especially the numpad ones
(e.g., `.` is now `Numpad .` to distinguish from the regular `.`
period).

Breaking change: if the user never had `P1 Keypad 00` set, the default
will change from `Enter` to `Numpad -` since both enter keys trigger the
same. This will affect a small number of popn/ddr players. They can just
change it back.

## Testing
*how was the code tested?*

src/spice2x/cfg/button.h

@@ -49,6 +49,10 @@ private:
     std::string name;
     std::string device_identifier = "";
     unsigned short vKey = INVALID_VKEY;
+
+    // default bindings are always naive
+    unsigned short vKey_default = INVALID_VKEY;
+
     ButtonAnalogType analog_type = BAT_NONE;
     double debounce_up = 0.0;
     double debounce_down = 0.0;
@@ -125,6 +129,14 @@ public:
         this->vKey = vKey;
     }
 
+    inline unsigned short getVKeyDefault() const {
+        return this->vKey_default;
+    }
+
+    inline void setVKeyDefault(unsigned short vKey_default) {
+        this->vKey_default = vKey_default;
+    }
+
     inline ButtonAnalogType getAnalogType() const {
         return this->analog_type;
     }