Orders Widget: add message if sorted by Side

When the orders widget is sorted by Side, it shows only Buys (Asc) or Sells (Desc).
If one side has no orders for that Market, it's not obvious why no orders are visible.

Suggest a note is added to the widget when the orders are sorted by side saying that "Only Buy OR Sell orders are shown when orders are sorted by Side."
or "Click the Date column header to see all orders".
Or similar.