M300433/number conversion improvement

When implementing the conversion functions std::numeric_limits::quite_Nan() was used. Since this Nan is only defined for floating point types the implementation was wrong. When adding the tests contained in this PR this was found and fixed.

• added tests for handling of empty strings
• split number conversion into two functions (integral/floating)
• added exception on wrong conversion
• the two new functions catch this exceptions and return ::max() for integral and ::quite_Nan for floating point representations

requested review from @m214003

assigned to @m300433

added 4 commits

• af75a2a6 - 1 commit from branch develop
• 9019945d - fixed str to integral number converision returning nonexistent NaN
• e2541047 - added tests for empty strings and other failure tests for number conversions
• c271fbd7 - option missval now uses string_to_floating

Compare with previous version

merged