Issue #2957425 by tedbow, johndevman, tim.plunkett, hawkeye.twolf, Berdir,...

Issue #2957425 by tedbow, johndevman, tim.plunkett, hawkeye.twolf, Berdir, alexpott, samuel.mortenson, kevincrafts, jibran, larowlan, amateescu, twfahey, sjerdo, mtodor, japerry, xjm, phenaproxima, mglaman, EclipseGc, johnzzon: Allow the inline creation of non-reusable Custom Blocks in the layout builder

(cherry picked from commit 500403b4)