feat: terrain is now selectable

What are the key features of this change

Added a button to change the terrain. Lists the enums from Terrain. Also set a standard font size to minimum 20px. Buttons are set to 20pt = 26px. Made buttons for resetting and running the battle disabled if both armies are not imported. Updated som javadoc for battle

closes: #19 (closed)

Size of change: medium

Checklist

• Javadoc is added to methods and classes
• Tests are added to feature
• Build tool test passed

This image shows the disabled buttons.