Split functionality for ReportFdaSampling

[edvinf]

The output for ReportFdaSampling is structurally different depending on whether the argument 'SamplingVariables' is provided (see function documentation for ReportFdaSampling). This behaviour is by design, as users like to have one place to consult for these nearly identical outputs. But I think it was a mistake. Users will easily get confused about what total weights of the fishery is, and functions that consume this data-format have to check for which variant is passed.

Downstream functions in StoX are at the moment:
PlotSamplingCoverage
PlotSamplingOverviewCell
PlotSamplingVariables

Each of these require sampling variables to be either present or not. ReportFdaSamplingData should clearly be two data types. We should consider fixing this the next time we are deciding to break backwards compatibility.