Issue #2549801 by quietone, balagan, lostkangaroo, pingers, martins.kajins, phenaproxima, scuba_fly, penyaskito: Improve source provider missing exception message

Issue #2471739 by RajeevK, martins.kajins, pektinasen, LewisNyman, jaxxed: Convert reusable layout classes to BEM standards

Issue #2576037 by unqunq, er.manojsharma, sdstyles, martins.kajins, Devaraj johnson, cilefen, Bojhan, Wim Leers: "Sorry" in user-facing errors violates the User Interface Standards

Revert "Issue #2471739 by RajeevK, martins.kajins, LewisNyman, jaxxed: Convert reusable layout classes to BEM standards"

This reverts commit cec8f5eb.

Issue #2511036 by martins.kajins, mdrummond, Cottser: image-widget.html.twig never gets used (image_widget gets overridden by FieldWidget::process)

Issue #2471739 by RajeevK, martins.kajins, LewisNyman, jaxxed: Convert reusable layout classes to BEM standards

Issue #1085472 by kpun, emma.maria, corbacho, rudraram, martins.kajins, briandev: Long strings within comments break Bartik's page layout