Add new settings & configuration options

[Arignir]

• [ ] Emulation
  • [x] Import save
  • [x] Export save
  • [ ] Change the save directory
  • [ ] Change the quicksave directory
  • [ ] Raise the maximum amount of recent files up to 10
  • [X] Rename "max speed"/"unbounded speed" to "fast forward"
  • [x] Support partial speeds (25%, 50%, etc.)
  • [X] Raise the maximum amount of quicksaves up to 10
  • [ ] Enable/Disable the emulation of the prefetch buffer
• [x] Video
  • [x] Enable BG layer X
  • [x] Enable OAM
• [x] Audio
  • [x] Enable Channel X
  • [x] Enable Fifo Channel X
• [ ] Misc
  • [x] Pause the game when the windows looses focus
  • [ ] Automatically resume the last played game on startup
  • [ ] Hide cursor after X seconds of inactivity
  • [ ] Hide menubar after X seconds of inactivity
  • [ ] Screenshot path
  • [ ] Text/Alpha when paused
  • [ ] "Press any key to leave pause"
  • [ ] Show FPS
• [ ] Bindings
  • [ ] Toggle the settings menu
  • [ ] Raise/Reduce the speed by X%
  • [X] Quicksave bindings for all quicksaves
  • [X] Mute sound
  • [ ] Raise/Lower the volume by X%
  • [ ] Hide menubar
  • [ ] Allow key modifiers in bindings (ctrl/alt/shift)
  • [ ] Set the default bindings for quicksaves to 1..0
• [ ] Cancel/Reset buttons
• [x] Implementation
  • [x] Revamp the code to have a settings struct that you can compare against and restore
  • [x] Use a common message to set all the runtime-related settings (speed, video/audio layers, etc.)