Minor Fix to Mouse Re-Capturing

Another small update, thanks to feedback from some kind testers.

• Added a way for the game to automatically check mid-scene whether the mouse needs recapturing.
• Added the M key (as in Menu) to the keybinds for opening the pause menu. Closing the pause menu forces a mouse recapture, but it was previously bound only to Tab and Escape, both of which can be problematic in browsers (Escape mainly).