Solid Boolean node: upgrade

Created by: portnov

• Support input nesting level 1 or 2.
• add ability to calculate which edge and face of the resulting Solid came from which source object(s). This is done via generalFuse method.

The following illustrates how EdgeSources output is calculated:

Here we have two cubes, 0 (plugged into Solid A input), and 1 (plugged into Solid B input). Purple edges came from cube 0, for them EdgeSources output contains [0]. Orange edges came from cube 1, for them EdgeSources output contains [1]. Edges marked with cyan came from both cubes, for them EdgeSources output contains [0, 1].

FaceSources output is calculated similarly, but for faces instead of edges.

• Code changes complete.
• Code documentation complete.
• Documentation for users complete (or not required, if user never sees these changes).
• Manual testing done.
• Unit-tests implemented.
• Ready for merge.

@vicdoval you might want to make a review.