Chemicals Refinery added

The last refinery - Chemicals Refinery - also added to the game. This generates rockets from explosives for the Rocket Turrets.

Now all buildings have been created and they function as they intended (UI is still missing the Chemicals Mine and Refinery images, but they will be added soon). With the buildings ready, I will need to finish the remaining 3 turrets, then play testing and fine tuning of the management system will come.