Issue #2283969 by tim.plunkett: Add a protected BlockBase::blockAccess() to contain plugin-specific logic.

Issue #2228941 by larowlan, andrei.dincu | Cottser: PHP notice displayed for forum blocks when there are no forum topics.

Issue #2158003 by Wim Leers, msonnabaum, effulgentsia, moshe weitzman: Remove Block Cache API in favor of blocks returning #cache with cache tags.

Revert "Issue #2020387 by mr.baileys, Andi-D, dawehner, oadaeh, YesCT, Kars-T: Convert 'Active forum topics' block to a View."

This reverts commit d166be36.

Issue #2020387 by mr.baileys, Andi-D, dawehner, oadaeh, YesCT, Kars-T: Convert 'Active forum topics' block to a View.

Issue #1951386 by benjy, theduke, andypost, tim.plunkett: Fixed Extend BlockPluginInterface::access to allow passing in an account.

Issue #2062573 by claudiu.cristea, tim.plunkett, Xano: Change notice: Add method defaultConfiguration() in ConfigurablePluginInterface.

Issue #1927608 by EclipseGc, tim.plunkett, effulgentsia: Remove the tight coupling between Block Plugins and Block Entities.

Issue #1987298 by tim.plunkett, quicksketch: Shorten directory structure and PSR-0 namespacing for plugins.

Issue #1535868 by EclipseGc, tim.plunkett, xjm, Jody Lynn, sdboyer, naxoc, tizzo, effulgentsia, dawehner, disasm, beejeebus: Convert all blocks into plugins.