* Improve naming for root scene graph switch/separator nodes.
* Improve scene graph inspector.
This commit improves the scene graph inspector by improving the UI
layout and displaying information in a more human-readable way.
Instead of having a main generic string column for all node-specific
data, introduce specific columns for node name, memory address and data.
Better visualization was also added for `SoDrawStyle`, `SoPickStyle`
and `SoCoordinate3` node types.
This patch substitutes by isAttachedToDocument() (almost) everywhere where
getNameInDocument() is used for this purpose.
The very few places not touched by this patch demand a (just a little) less trivial change.
When we change the returning type of getNameInDocument() to std::string,
those places will be easily found, because they shall generate a compiler error
(converting std::string to bool).
Rationale:
The fact that getNameInDocument() return nullptr to indicate
that the object is not attached to a document is responsible for lots of bugs
where the developer does not check for "nullptr".
The idea is to eliminate all those uses of getNameInDocument() and, in the near future,
make getNameInDocument() return always a valid std::string.
