You can now register a GWidget subclass with REGISTER_GWIDGET(class)
and it will be available for factory construction through the new
GWidgetClassRegistration interface.
To obtain a GWidgetClassRegistration for a given class name, you call
GWidgetClassRegistration::find(class_name). You can also iterate over
all the registered classes using GWCR::for_each(callback).
This will be very useful for implementing a proper GUI designer, and
also in the future for things like script bindings.
NOTE: All of the registrations are done in GWidget.cpp at the moment
since I ran into trouble with the fricken linker pruning the global
constructors this mechanism relies on. :^)
You now have to pass an Orientation to the GSlider constructor. It's not
possible to change the orientation after construction.
Added some vertical GSliders to the WidgetGallery demo for testing. :^)
Regardless of mode, made the knob container clickable so the knob position
can be moved without dragging the knob itself.
Added a 3rd GSlider to the WidgetGallery showing the proportional mode in
action.
