Change-Id: Ia3f85f0d0ccf18993dbbdd63ede5ec4fa963da79

HT are now indexed in such a way that there is no more
dead index.
HTGSource in quadric mode use the GlobalIndexStart mode to
avoid the storage of the local to global node id per tree
(contrary to descriptor/mask sources which use a BSF global
indexing mode, quadric nodes are numberered on a per-tree
basis).

Also remove some no more used functions and vars.

Change-Id: Ie5fe5f267a22706334d883d330b8aa9bbb3926e2

This global breadth-first search let the user access to point
data in the same order as in the descriptor which describes
the tree representation in BFS.
Moreover, each tree node (even non-leaf ones) can now have
data attached. As previously, the dual only address the tree
leaves.
Updating source, filters and tests to take advantage of this
new behaviour.

Change-Id: I4998336e38cc2d5cf79ec50e51ecc877cb74077e

Change-Id: Ib73de685956f4ef4d2b9dfb9ce8e4561ae9df945

- Replace the vtkCollection which has a find access in O(N) by a std::map.

- Add vtkHyperTreeIterator to avoid browsing every potential tree of
level 0 grid. Only available trees are now browsed.

- Add a TimeStamp to avoid unnecessary calls to the costly
UpdateHyperTreesLeafIdOffsets.

Those 3 changes really improve the computation time for building the HTG
but also for computing the dual and all the filters
(AxisCut, Geometry & ToUnstructuredGrid).

Also add points for each cell in the tree, not only for leaf, even if
only leaf points are used to construct the dual and thus referenced by
some cells.

Change-Id: Ie954fdc8860a55d0de9c23097b0662a2d2123550