#5 building's materials, workshop menu and some bugs fixes

Hi ! 

Today I added a building material menu, which are generated randomly and that you can assign to each building. Later they will be created in function of the resources you own.

You can now add for each tiles 4 walls, corresponding to the 4 cardinal directions.

I also made improvements of the UI, and made a proper workshop UI.

Some bugs due to the infinite chunk terrain were also fixed, but I'm sure there still plenty of them, hehe.