Correct development with only allowing memb_dim and time_dim to be different between data1 and data2; improved documentation; added unit tests

Improved development of MergeRefToExp; improved documentation; added unit tests for the new development

Add in documentation that in result, the Dates correspond to the beginning of the aggregated time period

Add time_bounds in functions that reduce time dimensions ; Add  element; Add checks if dates have dimensions; add tests for this development

Develop new element time_bounds with start and end elements containing the start and end dates of the aggregation for PeriodMean and PeriodAggregation; updated documentation; added tests