Move a function definition
Collect contributions of all authors

Each contribution has a reference to its parent author.
Filter contributions instead of authors

I intend to configure custom functions to reduce selected contributions
to the number of distinct authors instead of the number of contributions.
Display the number of authors rather than the number of contributions

The change is currently limited to the Data Count Widget, and I intend
to make the same change in the bar chart for total assessment reports
and the row chart for working groups.
Create a separate state for each set of custom functions to count authors

This will allow to use the same approach on each dimension without conflict.
Count authors, not contributions, in bar chart and row chart
Increase margin to the right of the row chart
Display donut chart below associated pie chart
Reset author selection in initialization function
Only display 25 authors while interacting with other charts

I intend to display the full list of authors only when requested
explicitly by the user.
Disable elasticX in Row Chart to keep a fixed reference
Display labels of row chart in dark gray (again)
Disable elastic scale in bar chart to keep fixed reference
Add debug code to identify the origin of negative counts in row chart
Use values with a custom state in crossfilter accumulators

The values need to be unwrapped for external access,
which required to monkey patch the methods used in dc charts.
Remove empty line
Use custom value accessor instead of monkey-patching where possible

I still had to intercept the call to groupAll.value() which was not
affected by the value accessor.
Create a distinct state in each accumulator

This fixes the issue which resulted in negative counts in Row Chart.
Remove scaffolding used in debugging
Remove unused contribution id