This patch refactors the Scene properties to use the Grid Flow layout.

• Keys Set panel refactor - introduce the Keyframing Settings sub-panel

• Rigid Body World refactor - introduce the Settings sub-panel as with all the items expanded uses a lot of vertical space Note: the Cache sub-panel will also be affected in the Physics area.

• Custom Properties are fully flowing now

Custom Properties expanded	Single	Rigid Body World expanded	Single	Key Sets expanded	Single

Some of the of the current issues are not addressed and noted in the code.
The current issues are:

• Some of the properties will have the animation entry dot on the right even though they cannot be animated. Those have skipped / disabled the property decorate for now
• Operators buttons are still not using the single column split.
• Use Curves sub-panel uses the template_curve_mapping that needs to be edited elsewhere.
• template_any_ID doesn't have the label right aligned for now.