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/event/extent/EditSessionEvent.java

@@ -23,10 +23,10 @@ import static com.google.common.base.Preconditions.checkNotNull;
 import static com.sk89q.worldedit.EditSession.Stage;
 
 import com.sk89q.worldedit.EditSession;
-import com.sk89q.worldedit.Vector;
 import com.sk89q.worldedit.event.Event;
 import com.sk89q.worldedit.extension.platform.Actor;
 import com.sk89q.worldedit.extent.Extent;
+import com.sk89q.worldedit.math.BlockVector3;
 import com.sk89q.worldedit.world.World;
 import com.sk89q.worldedit.world.block.BlockStateHolder;
 
@@ -53,7 +53,7 @@ import javax.annotation.Nullable;
  * is set to {@link Stage#BEFORE_HISTORY}, then you can drop (or log) changes
  * before the change has reached the history, reordering, and actual change
  * extents, <em>but</em> that means that any changes made with
- * {@link EditSession#rawSetBlock(Vector, BlockStateHolder)} will skip your
+ * {@link EditSession#rawSetBlock(BlockVector3, BlockStateHolder)} will skip your
  * custom {@link Extent} because that method bypasses history (and reorder).
  * It is thus recommended that loggers intercept at {@link Stage#BEFORE_CHANGE}
  * and block interceptors intercept at BOTH {@link Stage#BEFORE_CHANGE} and