Improve OpenFormula-support

by Nityam Vakil for KDE

Calligra Tables supports the OpenFormula-specification to implement formula functions. To fully support all of the defined heighest level 4 we need to add support for following 18 formulas which are missing at the moment in Calligra Tables; averageif, averageifs, b, chisqdist, chisqinv, countifs, critbinom, dde, external, forecast, hyperlink, legacychitest, linest, logest, networkdays, percentrank, prob, sumifs. Every of those 18 formula should come with unittests to prove that the formula is working as expected. Also every of the formula needs to have documentation so it can be added/edited from within the UI.