Added sensitivity slider!

Hello, all!

I've gotten around to doing a very small update today, which is:

a mouse sensitivity slider!

I know pretty much everyone's been struggling with the default sensitivity for the game, so I made it so that you can customize it in game through the pause menu! (Btw, for those wondering, that default sensitivity is literally just my usual fps sensitivity when I play games :] )

It doesn't save or anything, so you'll have to set it whenever you start a new alien encounter, but you now have full control over it!

Cheers,

Shakles