Issue #1591806 by tim.plunkett, ryanissamson, jenlampton, Risse, psynaptic, Gábor Hojtsy, kmcculloch, pakmanlh, Rob Loach: Change block 'subject' so that it's called (admin_)label like everything else on the theme layer.

Issue #1826602 by damiankloip, xjm, sun, dawehner, EclipseGc: Allow all configuration entities to be enabled/disabled.

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