Activated address-part code generation support.

sieve/tests/address-part.sieve

src/lib-sieve/ext-envelope.c

src/lib-sieve/sieve-address-parts.c

src/lib-sieve/sieve-address-parts.h

src/lib-sieve/sieve-code.c

src/lib-sieve/sieve-code.h

src/lib-sieve/sieve-validator.c

src/lib-sieve/tst-address.c