Previously, box style selection is rendered using customized
SoBoxSelectionRenderAction, which does not support selection context,
i.e. it does not work with Link.
This patch implements context aware bound box rendering inside
SoFCSelectionRoot, SoFCSelection and SoFCPathAnnotation (for always on
top rendering). The box rendering in SoBoxSelectionRenderAction is
disabled on construction. Box style selection can be enabled for
individual object through property SelectionStyle (moved from
ViewProviderGeometryObject to ViewProviderDocumentObject), or globally
through Parameter BaseApp/Preferences/View/ShowSelectionBoundingBox.
In addition, the parameter BaseApp/Preferences/View/UseNewSelection is
used to override selection model reported from
ViewProvider::useNewSelectionModel(). The reason being that, the same
parameter is already used to toggle selection model inside
SoFCSelection. This avoids inconsistency of selection model choice
between view provider and the SoFCSelection node inside. Note that if
the parameter 'UseNewSelection' is set to false, those view providers
that choose old selection model will not work with Link.
The patch implements context-aware selection and rendering in 3D view.
Please check [here](https://git.io/fjiY5) for more details, including
the following 'Render Caching' section.
The patch also includes modification of View3DInventorViewer to support
always-on-top selection rendering using the secondary selection context
and the new coin node SoFCPathAnnotation.
Another small change in SoQtQuarterAdaptor for more responsive frame
rate display. The original implementation reports skewed frame rate
in the presence of long idle period.
