Deprecated notify extension: implemented denotify command.

Makefile.am

src/lib-sieve/plugins/notify/cmd-denotify.c

src/lib-sieve/plugins/notify/ext-notify-common.h

src/lib-sieve/plugins/notify/ext-notify.c

src/lib-sieve/sieve-actions.h

src/lib-sieve/sieve-comparators.h

src/lib-sieve/sieve-result.c

src/lib-sieve/sieve-result.h

tests/deprecated/notify/denotify.svtest