On 22 Feb 2014, at 00:59, rog7993@web.de wrote:

Maybe I expressed it somewhat unclear. It was less a feature request for implementing a general link to the DAViCal admin page, than the question for a hint, where I could patch the code for my installation only.

you need to modify the index.html (and maybe add few lines of CSS) ... if possible, use absolute positioned div with your icon (because adding more "apps" to the menu div needn't work).