Clarify semantic of flatten Collections (walkthrough).

In the Cell/Instance hierarchy, the "terminal" and "leaf cell" concepts
where not clearly defined and partially overlapping. Now, "Terminal" is
the refer to the physical hierarchy (layout) and "TerminalNetlist" to
the logical hierarchy (netlist). The logical hierarchy can be less deep
than the physical one thanks to a Cell dedicated cell flags. Collections
related to the physical hierarchy keep their old names, the one related
to the logical hierarchy are renamed from "Leaf" to "TerminalNetlist".
The name "Leaf" was too ambiguous (leaf for *what* hierarchy).

* Change: In Hurricane::Device, set the "TerminalNetlist" flag once and
    for all. No need set it in all the derived classes again.
* New: In Hurricane::MultiCapacitor, added new parameter "dummy" to
    create dummies around the capacity matrix.
* Change: In Hurricane::Cell, remove "Leaf" related methods, replace
    them by "TerminalNetlist" one, especially Collections. Now we have
    two clear sets of Collections to walkthough the layout or the
    netlist.
      Change the "Terminal" flag into "TerminalNetlist".
* Change: In Hurricane::CellCollections, rename "Leaf" into
    "TerminalNetlist" collections and apply the new semantic to the
    locators.
* Change: In Hurricane::DataBase, Leaf to TerminalInstance renaming.
* Change: In Hurricane::DeepNet, Leaf to TerminalInstance renaming.
* Change: In Hurricane::HyperNet, Leaf to TerminalInstance renaming.
* Change: In Hurricane::Instance, Leaf to TerminalInstance renaming.
* Change: In Hurricane::Viewer::HierarchyInformations, Leaf to
    TerminalInstance renaming.
* Change: In CRL::AllianceFramework, Leaf to TerminalInstance renaming.
* Change: In CRL::Catalog, Leaf to TerminalInstance renaming.
* Change: In CRL::ApParser, Leaf to TerminalInstance renaming.
* Change: In EtesianEngine::AddFeeds, Leaf to TerminalInstance renaming.
* Bug: In EtesianEngine::resetPlacement, move there the loop over
    non terminal netlist instances to flag fully placed sub-blocks
    as terminal for the netlist. Only then remove the feed cells
    from unplaced instances. Previously, the feed cells where stripped
    even from already placed instances.
* Change: In Katana, Leaf to TerminalInstance renaming.
* Bug: In Bora::PyDSlicingNode, allow the range parameter to be the
    Python None object when we do not want to pass one but need to
    have it as positional parameter.
* Change: In Cumulus/clocktree/ClockTree.py, Leaf to TerminalInstance
    renaming.