Add turbo speed hotkey

[OpenSauce04]

Rebased from #455 by @kleidis

Closes #414

Adds a new turbo speed slider to the general tab along with a new hotkey which once pressed, toggles the frame_limit setting % to match the `turbo speed slider value. Once the hotkey the hotkey pressed again, it returns to the global frame_limit value the user originally had

A few changes were made to the original behavior as well (on QT)

• The frame_limit slider is licked at runtime
• • Due to the way the slider originally worked, leaving this changeable at runtime would cause issues with the hew hotkey also changing the frame limit setting key, meaning toggling to turbo mode also changed the global frame_limit value. So the most straightforward way I thought of fixing this was to just lock the slider at runtime and return the original non-turbo value once the game is closed
• Increase/ Decrease Hotkey also got changed to modify the new turbo speed key instead of the original frame_limit key directly like it was before
• • This makes it easier to restore the original frameskip value after the end of a gaming session