added date range sub-widget, works with bugs

Successfully re-querrries and re-draws the ledger within a date range on
the fly.
Currently the date range sub-widget works, but:
- redrawLedger text doesn't have a proper hook; It redraws inside its main
  div tag, instead of replacing it.
- the redraw breaks the jquery-ui dateselectors.
- the redraw does not calculate a startng ballance, based on entries
  previous to the selected range.