Remove my duplicate copy of the plane class, and add new methods.
Remove my duplicate copy of the plane class, and add new methods.

Moves d() implementation to the new definition of the class, which
is in the correct place (after Matrix4), and adds a couple other
convenience methods.

git-svn-id: 83c4c97093aeea62ac982fbfd516bf9db27f5c99@788 c36c8488-0289-0348-9b64-b301f74bd9a7

BlueBrain/Tuvok,BlueBrain/Tuvok,BlueBrain/Tuvok