Issue #3304256 by longwave, Spokje, dww, lauriii, catch, quietone, mherchel: Remove Bartik from Drupal core

Issue #1014086 by catch, nod_, martin107, quietone, dww, mariacha1, Spokje, yogeshmpawar, pounard, Wim Leers, mfer, mikeytown2, mbutcher, moshe weitzman, Fabianx, borisson_, alexpott, donquixote, sun, andypost, dawehner: Stampedes and cold cache performance issues with css/js aggregation

Issue #2665992 by alexpott, klausi, heykarthikwithu, xjm, tstoeckler: @file is not required for classes, interfaces and traits

Issue #2597359 by Wim Leers: Require responses with attachments to contain the final attachment values

Issue #2368797 by Wim Leers, dawehner, rteijeiro: Optimize ajaxPageState to keep Drupal 8 sites fast on high-latency networks, prevent CSS/JS aggregation from taking down sites and use HTTP GET for AJAX requests