Remove duplicate export of total contributions categories
Separate institution id from country id in contribution code

I had to introduce an intermediate table, institution_countries,
extracted from institutions table.

To avoid confusion, it would be better to create two separate
table to replace the current institutions table:

* institutions: id, name, institution_type_id
* institution_countries: id, institution_id, country_id

After this change, all fields referring to the current
institutions.id field shall be renamed from institution_id
to institution_country_id, while keeping their value.

The data for each table can be extracted from existing data
with following queries:

-- extract institutions
SELECT
  MIN(id) 'id',
  name,
  type_id 'institution_type_id'
FROM institutions
GROUP BY name
;

-- extract institution_countries
SELECT
  institution_countries.id 'id',
  institutions.id 'institution_id',
  institution_countries.country_id 'country_id'
FROM
  (
    SELECT
      MIN(id) 'id',
      name
    FROM institutions
    GROUP BY name
  ) institutions,
  (
    SELECT
      id,
      name,
      country_id
    FROM institutions
  ) institution_countries
WHERE
  institutions.name = institution_countries.name
;