ModelGeometry: set sensible values for "geom_density" min/max/default

[Maciej Komosinski]

http://www.framsticks.com/trac/framsticks/browser/cpp/frams/model/geometry/modelgeoclass.cpp

Currently "0.01 100.0 1.0", yet a range 5..25 was used for initial tests while the source was in development.

Perform intensive tests for diverse structures to analyze the influence of density on estimated volume, area, sizes, and time of computation.

Consider introducing adaptive density - users would only set the maximal % of error, and this would be the basis for automatically adjusting density based on earlier off-line tests and discovered properties.