0031987: Visualization - Slow rectangular selection on models with big number of...

0031987: Visualization - Slow rectangular selection on models with big number of sensitives

SelectMgr_SensitiveEntitySet now stores a map of registered owners with a counter of registered entities.
SelectMgr_ViewerSelector::traverseObject() now reads the number of sensitive entities for specific owner
from SelectMgr_SensitiveEntitySet instead of re-computing it every time.

(cherry picked from commit 266877a7c3963b4ac02bb1d015e74b405244d80e)
(cherry picked from commit 86d48bca1ae8a63ecf096845464bfd332d20d47c)
(cherry picked from commit 21351d74ac5a7c61a89c0cfe701f1d4ce1a8219f)