Issue #2688945 by tduong, amateescu, timmillwood, alexpott, joachim, xjm,...

Issue #2688945 by tduong, amateescu, timmillwood, alexpott, joachim, xjm, yoroy, ifrik, Berdir, Gábor Hojtsy, Bojhan, webchick, cilefen, dawehner: Allow removing a module's content entities prior to module uninstallation