and here are the three files for my mod and a short how-to:

(0. make a backup of the original files! ^^)
1. place a picture with 60x60 in /usr/share/rtcom-messaging-ui/html/ named "avatar.png"
2. replace the three files (html, css, js) in the same folder with my modded files

i tried for about one hour to get absolute paths to work but it doesn't seem to work. so i had to place the png in the html-folder.
also the method which is used for fetching the pictures of the contacts doesn't seem to work for the own avatar - and it's not clickable too. ^^