Flagging of blocks as fixed displays

  Some initial work on calculating the position of the fixed displays.
    These calculations have to occur after the flow tree has been
    initially constructed because the containing block might have a
    height of auto.
Fixed recognition of fixed displays.
Position based upon the initial containing block

    Have yet to actually remove fixed displays from the actual flow.
    finished positioned box offsets.
Position fixed displays out of normal flow.
Small fix to support percents