v5.4.7

• proper mime encode wrapping when sending emails with long utf-8 recipient names
• proper mime encode wrapping when sending emails with long utf-8 subjects
• reorganize help bar items in message list view
• fixes #179 - add support for server-side imap search
• set env variable required for default external html viewer w3m to use lessopen/lesspipe
• update doc with run-time dependencies for html emails
• add support for using external html viewer to view message parts/attachments
• switch to terminal-based default external html viewer