More colours, easier Start zone, bug fixes

This update changes the design from mostly purple to what I hope is a consistent palette of several colours.

After getting feedback from players the Start zone is too hard, I moved the Sentinels around. It should now be easier to navigate around the map.

I also got feedback moving around on a touch device wasn't working great. I've introduced a new virtual "joystick" that works better and more reliably than the previous one. It works by being activated and then dragging in a given direction. The keyboard is still more accurate, but the touch navigation should work better now.

I fixed a few bugs too:

• Page scrolling and hiding a portion of the screen
• Mission to Build a Heal Station could not be completed (now it can)
• The Landing in the Start zone was not spawning in its correct location (now it does)

If you have any feedback, let me know in the comments! Thanks for trying my game as it's being developed :)