More GUI, Blorb Collection, Optimization, Selling

The only mechanic left to implement is that enemies should get mad and attack towers when there is no path to the center of the base.

• The GUI is now equipped with explanations for each of the towers
• Tower placement is more obvious and intuitive to the user
• You can sell towers, and the game correctly handles the selling of all towers attached to the base by the tower you are selling
• Blorb collectors now function, and turn resource tiles into mountains once all the blorb has been drained
• Much more!