7212: GridLayer
7213: refactor
7215: grids
7216: update IParentLink
7218: prepare UIGridBox sample
7220: UIElement.GetPrimaryRenderElement

remove UIElement.PrimaryRenderElement
7221: UIBox
7223: rename LayoutFarm.Presentation

just LayoutFarm
7206: remove VisualLayer.AddTop()
7207: update GridBox sample

rename CanvasBase to Canvas
rename GridItem to GridCell
7228: GetGridItemByPosition

update , clamps x,y
add UIBox to Grid
7227: refactor
Merge branch 'v_grid' into v1.7