Several CA fixes

[marc-vdm]

Add:

• CA data: use actual total instead of sum(abs)
• CA data: make distinction between positive and negative rest values (resolve Contribution graphs > Rest should be split into positive and negative sections #886)
• CA data: sort based on average of row instead of first column (resolve Sorting Contribution Analysis tables better #887)
• CA table: consistent dropping of empty (rest) rows (resolve Contribution analysis rest row sometimes doesn't show in table + index missing #1044)
• CA figure: add marker to show total score when both positive and negative results present (resolve Figure improvements 4/x - Contributions graphs with negative values #647)

Example:

TODO:

• update wiki (Styling updates + wiki page on contributions and sankey #1381)

Checklist

• Keep pull requests small so they can be easily reviewed.
• Update the documentation
  • For in-code documentation, please follow the numpy style guide.
  • For user documentation, please update the wiki in
    ./activity_browser/docs/wiki
• Update tests.
• Link this PR to related issues by using closing keywords.

If you have write access (otherwise a maintainer will do this for you):

• Categorize the PR by setting a good title and adding one of the labels:
  bug, feature, ui, change, documentation, breaking, ci
  as they show up in the changelog.
• Add a milestone to the PR (and related issues, if any) for the intended release.
• Request a review from another developer.

[coveralls]

coverage: 54.196% (-0.03%) from 54.228%
when pulling 21cb6e5 on marc-vdm:CA_updates
into 9d4a1c4 on LCA-ActivityBrowser:main.