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.
On Qt5, using pinch will inevitably cause tilt. It's annoying, so it is disabled by default.
In the future, it's best to introduce some kind of threshold to overcome for the tilt to be triggered.
Before that (e.g. on MacBook Pro) it was very hard to see the microscopic selection-circle hidden behind much bigger cursor arrow when trying to snap e.g. a line to some vertex. Now this setting can be used for such displays to increase the marker size and make it clearly visible behind the cursor.
The already existing "sketcher marker size" property is intended to be used for sketcher only, so it's not suitable for global setup of all the markers' sizes uniformly...
+ handle destruction of GL context in 3d viewer class
+ fix for OpenGL error message: 'Texture is not valid in the current context. Texture has not been destroyed'
*First step to move Part rendering using VBO instead of direct rendering
*Update comments inside the code
*Assume VBO is available if OpenGL > 3.0 is detected
*Add initial Color support to VBO rendering !
*Initial full feature VBO rendering implementation
*Modify some include issue for linux build
*Try to fix linux include header
*Reupdate header include for linux support
*Fix compilation on linux
*Fix linux and MacoOS build
*Fix glGetString definition
*Fix Windows build
*Add VBO support as an option into the Preference menu
*Fix crash while running FreeCAD test bench with new VBO rendering infrastructure (in both cases)
*Improve performances
*Compute material index only when a VBO update is required (improve frame rate by 10%)
*Clean the code
*Fix Travis compilation warning
*Try to fix Windows compilation issue
*Update include for Windows
