Add a check function for impact categories

[msrocka]

This would check the following things:

• If there are multiple factors for the same flow (and location) it would show an error and an option to remove the duplicates (in case of different factor values / formulas the user would need to decide which factor should remain in the impact category).

• For regionalized impact categories it would show an error when the default factor is not present (and maybe an option to add the default factors; but this should be something like an editable table in a popup dialog then).

• For flows with the same name and quantities that are located in sub-compartments (where unspecified is a top-compartment of the other compartments on the respective level) which do not have a factor yet it would propose to add the same factors as for the corresponding flows in the top-compartments. Again, this should show these factors in a popup dialog.(Not sure with different flows with exactly the same compartment, name, and quantity because this is a database issue. Maybe this could be a pre-check with the option for the user to remove the duplicates and replace them with the remaining flow if the duplicates are already used.)

Also, when adding a new characterization factor of a flow openLCA could propose to add also the same factor for corresponding flows in sub-compartments (maybe with an input box for the factor so that the user just has to enter the factor value / formula once).

Finally, but not related to this feature, we should try to replace the current table with an editable (and searchable) tree where the compartments are the inner nodes. Also, in regionalized impact categories the default factor could be the parent node of the location specific factors of the same flow then.