New geometry features

* ImageActor XOML tag has new Filled (bool) property which specifies the
filled / unfilled status of an actor, unfilled will be drawn with a
border
* ImageActor XOML tag has new CornerRadius (float) property which can be
used to specify the corner size of a rounded rect (note that RenderAs
must be set to 2) to force actor to be rendered as a rect
* ImageActor XOML tag has new Thickness (float) property which specifies
the border thickness for actors that are rendered unfilled
* ImageActor XOML tag has new RenderAs (int) property which specifies
how the actor should be rendered, 0 - normal, 1 - render as an arc and 2
- render as a rect / rounded rect
* ImageActor XOML tag has new PlaybackSpeed property which specifies how
quickly any attached bitmap animation will play back
* ImageActor XOML tag has new AnimFrames (array of its) property which
specifies the order in which bitmap frames are played back
* Brush XOML tag has new RectFrames property which is a list of x,y,w,h
rect frames that can be used to assign bitmap animations to actors