Allow Box to be defined using center of box as origin

[SergeDorna-Philips]

Support a box that has it's origin at the centre of the box instead of the top left.

  <Box Id="MyBox_Center">
    <CoordinatesDimensions>
      <CenterX>left</CenterX>
      <CenterY>bottom</CenterY>
      <Width>width</Width>
      <Height>height</Height>
    </CoordinatesDimensions>
  </Box>

Also, allow mix and match to define one dimention from the center and another from the side.

  <Box Id="MyBox_Mixed">
    <CoordinatesDimensions>
      <CenterX>left</CenterX>
      <MinY>bottom</MinY>
      <Width>width</Width>
      <Height>height</Height>
    </CoordinatesDimensions>
  </Box>