Builder v0.4

This new version mostly contains changes concerning multiple selections and groups. It should be more logical and consistent now.

It does however also contain some new things, the most noticeable thing is that the way blocks are created have been changed. They are now easier to move away from the middle than they were before (you basically had to dig them out behind any other blocks you might have covering the middle). Another change is that the camera's view with left+right mouse-buttons will now retain the camera's relative position to its focal point.