Merging Cubes: Merge more than 2 cubes, different set of shared dimensions

[ptbrowne]

• Application error when adding a 3rd dataset (selected Median electricity tariff per canton, median electricity tariff for Switzerland, when adding Photovoltaik data set the application error is generated)

I think this is due to different shared dimensions between the cubes since

• Median canton and Median Swiss only share period
• When Photovoltaik is added it is selected with both cantons & period

A workaround is to deselect canton from the search options when adding photovoltaik.

Unclear yet to do when we merge more than 2 cubes that do not have the same set of shared dimensions. I think we should "fix" the set of shared dimensions from the first two.