Added partial support for the depricated notify extension.

src/lib-sieve/plugins/enotify/Makefile.am

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

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

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

src/lib-sieve/sieve-ast.c

src/lib-sieve/sieve-ast.h

src/lib-sieve/sieve-extensions.c