Backtesting Settings

Be able to set them, specially the Spread Pips, the plugins seems to be able to do it, but it is not possible in a cBot (in the code).

This would make a multi symbol bot useful, for now all the symbols takes the spread set in the UI, so for example if I set 0 for EUR USD, another symbol with a 500 spread won't work.

I know the ticks could manage it, but the backtesting is insanely slow, to do quick backtestings (getting gross strategy performance) a manual Spread Pips would be awesome, and it seems it is already implemented, just not for the backtesting code.

Ref: BacktestingSettings/#spreadpips