Visual Boy Advance - M Beta-3 Keyboard fixes

GBA/GB(C)模擬器 VisualBoyAdvance - M 發布新版，更新如下:

Apparently in some configurations, holding a key on the keyboard makes
Wx stop processing Idle events, so the emulator does not run until the
key is released, freezing the game and ignoring the key.
Hopefully fix this by calling wxWakeUpIdle() from OnKeyDown() and
OnKeyUp().
Other Misc. Improvements:

• refactor process_key_press() to only return true if the system is in a
  pressed key state on key presses or a game key was released on
  releases and always true on double releases.
• call ev.StopPropagation() from OnKey* events for game keys, this may
  not actually do anything, but just in case.
• remove static OnKeyUp and OnKeyDown events from GameArea, these are
  connected to the DrawingPanel dynamically now.
• remove the dynamic_cast<>s from PaintEv/EraseBackground/OnSize event
  forwarders, since there is already a panel member to use.

TODO:
The state returned by process_key_press() is still not entirely correct,
if a joystick button is pressed, it will return true for a non-game
keyboard press, and it needs to return the correct state for double
releases.

https://github.com/visualboyadvance-m/visualboyadvance-m/releases