Added structure for list of Cells and point Ids.

Added an std::vector to hold, for each cell, the triplet of point Ids
corresponding to the vertices of that particular triangle. Related the
pointIds to positions in the std::set that de-duplicates points.
Implemented ReadPoints(buffer).

Now package the information about point coordinates into a buffer
that is passed back to the MeshFileReader.

Adjusted the helper data structures that hold the pointIds and the
iterators to unique points in the a point set.