Added Input System

[Chizaruu]

Added Unity's New Input System for more functionality.

Changes -

• Converted old Input keycodes to new input system in NewPlayer.cs
• Added more PauseMenu Support (You can use Escape to get in and out of it now)
• Changed PhysicsObject's Rigidbody protected state to private as protected isn't compatible with the new input system. (Reasons)
• Slight changes to Prefabs (I added Rigidbody2D to their appropriate fields.)

Feel free to ignore it if it doesn't suit the content.

[Chizaruu]

Can we take a look at getting this approved and merged?

I don't think he checks GitHub that much based on his commit history...

If you want the changes now, feel free to use my fork @jrhager84 https://github.com/Chizaruu/SuperSimple2DKit