Major rework of envelope address handling: a normalized version of the envelope addresses is maintained in the message context and message context is now also available during action execution.

Merged mail-raw implementations of sieve commandline tools and the testsuite, thus removing duplicate code.

Added the concept of a script code header to list the extensions actually used by a script (was using all extensions listed in the binary).

Body: added test regarding empty bodies and fixed testsuite to flush the message context when the message is changed.

Significantly improved handling of old/corrupt binaries and revised matching implementation in the process.