lib-sieve: Implemented support for generic Sieve storages.

TODO

configure.ac

src/Makefile.am

src/lib-sieve/Makefile.am

src/lib-sieve/plugins/include/cmd-include.c

src/lib-sieve/plugins/include/ext-include-binary.c

src/lib-sieve/plugins/include/ext-include-common.c

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

src/lib-sieve/sieve-binary.h

src/lib-sieve/sieve-common.h

src/lib-sieve/sieve-error.c

src/lib-sieve/sieve-error.h

src/lib-sieve/sieve-script-dict.c

src/lib-sieve/sieve-script-file.h

src/lib-sieve/sieve-script-private.h

src/lib-sieve/sieve-script.c

src/lib-sieve/sieve-script.h

src/lib-sieve/sieve-storage-private.h

src/lib-sieve/sieve-storage-sync.c

src/lib-sieve/sieve-storage.c