[Tree widget]: Adjust categories tree visibility handler methods

[JonasDov]

Prerequisite for #1362
Changed categories tree visibility handler methods.

1. Renamed all visibility change methods to: change<SomeType>VisibilityStatus.
2. Renamed all visibility get methods to: get<SomeType>VisibilityStatus.
3. Used Id64Arg instead of Id64Array | Id64Set.
4. Hierarchy config no longer changes how visibility is determined. In all cases we check elements and subCategories.
5. Added getModels, getCategories, getSubModels, getSubCategories, getElementsCount methods which will be needed when models, category and classifications visibility handlers are merged.
6. Updated get and changed methods, they can now be used in other visibility handlers.*

*All updated methods will be almost the same when models, category and classifications visibility handlers are merged. Only minor changes will be needed from this point.