Make work package table headers accessible and display them with temporary style (#2264)
Add change log entry (#2264)
Fix selection in integration test...


...after more than one table on work_pakages#show has table headers
Render relations table only if there are related work packages
Adds localizations
Introduces an image with an alternate text
Re-implements group toggle in jQuery
Hides expand/collapse all button for text reader
Adds changelog entry
Uses icon font instead of expand/collapse image
Removes superfluous locales
Show / hide work package relations table after AJAX updates


Fixes integration tests
Merge pull request #810 from opf/accessible-work-package-tables-2264
Fixed a small bug in mailer views
Merge pull request #819 from opf/fix/accessibility_alt_text_collapse_expand_on_grouped_work_package_list

[FIX] Accessibility alt text collapse expand on grouped work package list
Merge remote-tracking branch 'origin/dev' into fix/activity-icon-labels-2250