Restructured store action implementation to properly handle an attempt to store (keep) a message in the folder it originates from.

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.

Improved result execution and prevented failure on store action on dry run (with no specified namespace).

Properly implemented the code dumper. Dumps are now printed in a stream. The individual opcode and operand implementations no longer use printf()s.

Exported sieve-code-dumper from sieve-interpreter containing all code dumping related implementation. Now to remove all printfs....

The :flags tag introduced by the imapflags extension now attaches side-effects to the appropriate action commands.