lib-sieve: sieve-script - Restructure script sequence initialization

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

src/lib-sieve/sieve-script.c

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

src/lib-sieve/sieve-storage.c

src/lib-sieve/sieve-storage.h

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

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

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

src/lib-sieve/storage/file/sieve-file-script-sequence.c

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

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

src/lib-sieve/storage/ldap/sieve-ldap-script.c

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

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