Only raises an error message when user tries to use visualise_single_pair in multipair universe without providing pair argument in decide_trades, this should be far less breaking, if at all, than always raising.
Some small refactoring for visual util functions
The legend still shows for all pairs, have opened ticket #968 for this
visualise_single_pairin multipair universe without providingpairargument indecide_trades, this should be far less breaking, if at all, than always raising.