Many updates

Some new functionality has been added to DBM Knight's Tour.

Can now select:

Difficulty (grid size)
Tour Type (open or closed)

Start Position (Random, You Pick)

Still working on the responsive updates on mobile but it is playable.

I still need to add some validation to the random placement, like making sure you aren't placed in a position you can't win from.

Victory condition should honor closed tour conditional.

Appreciate any feedback and/or recommendations for handling responsive updates for mobile. This is my first time devoting time to rust/bevy but I want to make it my go to.