Add comment in hud
Fixe: Bad square rendering at the edges of the screen
Rename RenderSelection() to RenderSquare()
Order has a 'completionStatus' attribute accessible from unit interface + Clamp() templated
Renderer: new procedure RenderProgressBar()
HUD rendering is splitted into smaller methods
HUD: Training unit render a progress bar
World: new method BuilderOf(UNIT)
Fixe: 'completionStatus_' is set to 0.0 when building start being constructed
HUD: Render progress bar of building in construction