mrc-6301 area settings

[EmmaLRussell]

This branch adds the second stage of the load project stage, where, having loaded an input file, the user selects configuration options about how the file should be interpreted as to area identifiers, as per the mockups.

The config options are:

• whether the file contains regional values for a single country or multiple countries
  • if the former, the user chooses the country from a drop-down
  • if the latter, the user chooses a column in the file which identifies the country for each row, and also whether the countries are identified in the file by name or ISO3 code
• which admin level the regional values are for - Admin1 or Admin2
• whether regions are identified by name or GADM id.

We are currently supporting GADM41 identifiers only for names and IDs - other regional datasets, or allowing the user to bring their own may be added later.

In order to provide the list of countries, we fetch these from grout. Currently this is hitting the real grout server on mrcdata (which is fine just now as there are no other users of this!), but there's a ticket to run the grout dependency locally, and on CI, to test against.

This PR includes ConditionalAccordionItem, a "disable-able" accordion item to represent steps in the setup process which cannot yet be accessed because preceding steps have not been completed.

I've added a couple of test data files, multi_country_iso.csv and multi_country_name.csv.