Tutorial/Email System - v0.27.0

There's been an influx of new users recently so I decided to introduce a type of in-game tutorial in v0.27.0

You will receive an email introducing you to the game and explaining basic vehicle and camera controls. Then as certain events happen (tornado touches down, a populated area gets threatened etc.) you will receive an email explaining how that game mechanic works.

Hopefully this will stop players feeling like they're just "dropped in" to the game with no explanation what to do.

There have also been some fixes to tornado rendering and the vehicle materials.

Finally, I fixed the map tile with houses on: vehicle speed limits on and off road now apply.

As always, enjoy! :)