Removed test creature
Some cleanup:

- Implemented Equals and GetHashCode for Vec2 and Vec3 properly
- Removed the message box stuff in Game (to be replaced by a Panel)
- Map also doesn't log a block load message anymore.
Some cleanup and menu infrastructure
Added container infrastructure

With this infrastructure come some changes in the ways menus and panels
work, too.
Fleshed out picking up and dropping items.

This also involved fiddling with menus a bit more.