Added master-slave addressing for coupled points.

- Rewrote globalPoints to use globalIndex class so now only transfers
single label instead of labelPair
- Added addressing in globalMeshData
    - from coupled master points to slave points
    -         ,,          edges     ,,    edges
    - from coupled points (master or slave) to uncoupled boundary faces
    -               ,,                    ,,                      cells
- See test/globalMeshData for simple test