replaced DEFAULT_HOST by MAIL_DOMAIN
clarified MAIL_DOMAIN and MAIL_ADDRESS_PREFIX retrieval
clarified 'mimeremove' handling (Closes: #32)
added support for ezmlm-idx v5 features 'headerkeep', 'mimekeep' and 'copylines'
added 'easy' and 'expert' interface settings
fixed tagging of active menue items
cleaned version-specific visibility of some options (charset, language, ...)
