Moved the polygonization code to the specific regions that are being polygonized.

Also, maxPoints no longer has confusing semantics.
Reduced some code duplication in the regions.
Added a ConvexPolyhedralRegion and selector
Added the polyhedral selector to //sel.
Added constants to Vector2D, BlockVector and BlockVector2D and made the ones in Vector final.
Used vector constants in all appropriate placed.
Made BlockWorldVector.equals accept all kinds of Vectors, not just WorldVectors.

This should make all those compareTo==0 things unnecessary.
ConvexPolyhedralRegions now preserve the order of their vertices.
Add convex to the @Command usage info for //sel.
Only show nested commands in the Bukkit help if the player has permission to use at least one of the children
Tabs.
Merge branch 'master' of https://github.com/sk89q/worldedit