Add styles to tables in details-pane

- added styles to tables in details-pane
Merge branch 'dev' into feature/styleguide-details-pane-table
use detail-pane-table style for relations table
Development seeds: Make number of users configurable

Also, reduce default to 3 users instead of 30. I'm not into waiting 5 minutes
after setting up a new development database.

Set a SEED_USER_COUNT env var if you want more users.
Use generalised table styles for relations and attachments.
add titles for attachments and relations table headers.
Merge pull request #1717 from opf/feature/styleguide-details-pane-table
Merge pull request #1727 from opf/feature/faster_development_seeds

Development seeds: Make number of users configurable