Refactor vector system to be cleaner

- Move Vector, etc. into `.math` package
- Drop many methods that will be auto-promoted anyways, eg. with
`divide(int)` and `divide(double)` the first is now gone.
- Take Block vectors into their own class hierarchy
- Make it clear throughout the API what takes blockvectors
- many more improvements

worldedit-core/src/main/java/com/sk89q/worldedit/command/composition/DeformCommand.java

@@ -60,7 +60,7 @@ public class DeformCommand extends SimpleCommand<Contextual<? extends Operation>
             Player player = (Player) locals.get(Actor.class);
             LocalSession session = WorldEdit.getInstance().getSessionManager().get(locals.get(Actor.class));
             try {
-                deform.setOffset(session.getPlacementPosition(player));
+                deform.setOffset(session.getPlacementPosition(player).toVector3());
             } catch (IncompleteRegionException e) {
                 throw new WrappedCommandException(e);
             }