Also make some links more self-descriptive for accessibility reasons.
Remove trailing white spaces because my editor removes them
automatically (and yours should too).
Broken links were found with markdown-link-check with the following
command:
```
find . -name tmp -prune -o -name node_modules -prune -o -name \*.md -print0 | xargs -0 -n1 markdown-link-check
```
* Change of the integrations and community plugin page
* fix(docs): adjust links to moved pages; decrease image file sizes
* fix(docs): use https:// links where possible, remove unused images, unify lowercase file extension for pngs
* fix(docs): adjust links to moved pages; decrease image file sizes
Co-authored-by: birthe <b.lindenthal@openproject.com>
as-op