Progress: simple AI that walks around, multiple players

Notable features added:

  1. Units and cities auto-coloured to match Player colour
  2. Added turn management supporting multiple players
  3. In other players’ turns, popups + map tiles are disabled so you don’t see them
  4. AI is able to use the player’s Commands (e.g. Move, Build City)
  5. Added some basic AI for “if settler is on bad food square, move to a good one; if none available, move randomly and hope to find one”