Add logos for Skosmos 3

[UnniKohonen]

Reasons for creating this PR

Skosmos 3 is missing logos from all pages, this PR adds a logo to headerbar on landing page and to topbar on other pages.

Link to relevant issue(s), if any

• Closes #

Description of the changes in this PR

• Add .svg files for logos
• Add logo to landing page
• Add logo to other pages

Known problems or uncertainties in this PR

Headerbar (and thus logo) is visible on about and feedback pages, which should be fixed.

Checklist

• phpUnit tests pass locally with my changes
• I have added tests that show that the new code works, or tests are not relevant for this PR (e.g. only HTML/CSS changes)
• The PR doesn't reduce accessibility of the front-end code (e.g. tab focus, scaling to different resolutions, use of .sr-only class, color contrast)
• The PR doesn't introduce unintended code changes (e.g. empty lines or useless reindentation)

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (76d9ec5) 70.54% compared to head (52ee826) 70.54%.
Report is 1 commits behind head on skosmos-3.

Additional details and impacted files

@@             Coverage Diff              @@
##             skosmos-3    #1562   +/-   ##
============================================
  Coverage        70.54%   70.54%           
  Complexity        1644     1644           
============================================
  Files               32       32           
  Lines             4315     4315           
============================================
  Hits              3044     3044           
  Misses            1271     1271           

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[osma]

This is a terrible way of generating the link URL for the home page, but I see that it has been used in many other places as well (a few lines down in the same file) so I guess one more time doesn't hurt much.
However, I think a better mechanism should be developed. We already have the custom link_url filter, maybe it could be used instead, with some enhancements?

[osma]

Looks good and gets the job done. I commented about the URL generation, but that is a more general problem, not specific to this PR. I'll merge this as it is.