TODO:
- harmonize icon sizes where needed (some icons are 32x32, others are 22x22)
- harmonize style of icons to become more consistent
- other random improvements

VERSION HISTORY:
version 0.7: changed trayicons and new, unread and read icons for more consistency and less colors. reduced colors to red (ff0000), white and darkgrey (303030) only.
version 0.6: removed superfluous icons, replaced trash-icons. added key_gpg_signed.
version 0.5: cleaned up some more icons that looked ugly because of scaling. added a few icons (open_mail, checkbox_on/off, category, jpilot etc), so now it should be quite complete. also replaced some other icons (e.g. book).
version 0.4: cleaned up some icons that looked ugly because of scaling, harmonized/resized others, and replaced a few (e.g. addressbook, mail_attach, ham_btn, insert_file). added a few (e.g. ldap)
version 0.3: added dir_noselect and dir_close_mark and dir_open_mark, new address_book icon
version 0.2: added *hrm* and *mark* icons, harmonized offline status icons and trayicons
version 0.1: initial release