Get Market Spot Value
Function Get Market Spot Value within returns the default spot value under which the supplied quotable is supposedly quoted, before it is overriden by any user-supplied market data.
If a real time data provider exists, then this will be just the quote delivered by that provider.
On the absence of such a provider, a fixed value is returned, which is not the result of a calculation.
Note this value is used in the initial construction by Deriscope of relevant default market data.