Javadoc and Formatting fixes. (#619)

Javadoc and Formatting fixes.

Also, extremely minor code changes which have been tested.
This commit is only part one of two commits that aim to fix problems with formatting in our project. In part two I will modify the Google Java Style Guide (since it closely matches our code style) for our project so there is guidance on how to format and document. 

* Updated PlotSquared URL
* Removed plugin acronyms
* Fixed a typo
* Fixed grammar
* Use modern block id's
* Update YouTube video URL

worldedit-core/src/main/java/com/sk89q/worldedit/regions/CylinderRegion.java

@@ -274,7 +274,6 @@ public class CylinderRegion extends AbstractRegion implements FlatRegion {
      * Contract the region.
      *
      * @param changes array/arguments with multiple related changes
-     * @throws RegionOperationException
      */
     @Override
     public void contract(BlockVector3... changes) throws RegionOperationException {

worldedit-core/src/main/java/com/sk89q/worldedit/regions/RegionSelector.java

@@ -199,10 +199,10 @@ public interface RegionSelector {
     }
 
     /**
-     * Get the vertices
+     * Get the vertices.
      *
-     * @return
-     * @throws IncompleteRegionException
+     * @return the list of vertices
+     * @throws IncompleteRegionException thrown if a region has not been fully defined
      */
     default List<BlockVector3> getVertices() throws IncompleteRegionException {
         return Collections.singletonList(getPrimaryPosition());