additional contribution analysis fixes

[marc-vdm]

Changes

• Various changes to CA wiki page to improve wording and update on following points
• Subclass bw2analyzer.ContributionAnalysis to resolve bugs in original
• Resolves: Range/Score negative contributions plot bug #1429
  • Results were normalized in a wrong way, representing the result wrongly.
• Replaces Range with Score as default option in CA tabs
• The Total line in contribution tables is replaced with Score, which better represents what this actually means.
• Aggregate by categories for EF contributions is now actually resolved (EF Contribution Analysis > Aggregate by Categories broken #1385)
• Improved sorting of contributions, which now favours entities with single high contributions more (mean square)
• Add option to toggle score marker on/off

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: 53.087% (-0.2%) from 53.311%
when pulling ed7d705 on marc-vdm:ca_range_score_fix
into 1e02314 on LCA-ActivityBrowser:main.