Comparison fails if dataframe columns (ie indicators) don't all match, even if some do

[carlhiggs]

Describe the bug
The comparison feature currently allows comparison of results for overall study region summaries. This can be useful to evaluate macro impacts of data and analysis parameters that could represent methodological decisions (e.g. sensitivity analyses related to choice of data etc) or scenarios/interventions (e.g. modified data to represent these).

However, if one or more columns don't match, this will fail. There are a number of reasons why columns may not match. One is, using different linked data for different regions.

Expected behavior
The process should report back on all matching columns, and alert the user if some columns are not matching and therefore not compared.