Add SQL query to answer question 15

This is hierarchic data in nature, built with joins
with parent groups repeated in each result row.

This data is intended to be represented in treemaps,
with symbol columns only rendered with colors,
while other columns will display text.

The AR column is intended for aggregation and filtering:
a range of AR may be selected, and the corresponding
aggregate count of participations will be computed.
Add export of participations for use as a spreadsheet (Full Table)
Group participations by author and AR, like in original spreadsheet
Add queries to compute ratios of participation per country and chapter
Customize column headers of the list of French Authors
Customize column headers for ratios of participation (question 12)
Add label for each line, before the value

I also pluralized 'Participation' in column headers with totals.
Keep ratios instead of multiplying by 100 to get percentages

The percentage is only computed at display, by selecting Percentage
as a Number format in OpenOffice Calc.
Compute ratios of membership to bridge groups
Refine bridge ratios, using minimum of each group for the bridge value

This produces ratios which depict more accurately the membership
to the individual groups vs bridge groups.
Add missing multiplication factor for bridge groups: x2, x3

In previous ratio, only one of the groups part of a bridge
was counted, instead of all groups (up to the minimum of the
participations of the groups part of the bridge).

Due to rounding errors, some ratios appear off,
e.g. 0.99999 instead of 1. To reduce these rounding
errors, the division by the total number of participations
should be delayed until the last step.
Avoid rounding errors by delaying division by total

The error is reduced by dividing a larger number instead
of multiplying smaller numbers.
Order by each ratio in turn
Order bridge fields in same order as the sort

The fields used to be listed as ..., WG I+II, WG II+III, WG I+III, ...
while the sort is ... bridge12, bridge13, bridge23, ...
Compute ratios of roles in the context of bridge authors

The answer also includes the total number of distinct working groups,
distinct assessment reports and distinct roles in the participations
of each author, as well as the total number of participations.
Refined order of fields and projection and order clause

This is a long-standing modification, which I forgot to commit
at the time.