Create password-protected archives with Ark

This feature allows Ark to create a password-protected archive from
scratch.
The 7z and rar plugins support both header encryption and entries-only
encryption, while the zip one supports only the latter.

An encrypted archive can be created through the CreateDialog (within Ark) or
through the AddDialog (from e.g. Dolphin).

REVIEW: 120204
FEATURE: 253694
FIXED-IN: 15.08
GUI: