I've Modified my web-client-config-custom file to add icones. But I've got a problem: when I create my space by choosing an icon, I do not see any more the icones of smaller sizes in others spaces such "Shortcut" or "Recent Space"!!
I'm not sure if it's documented anywhere, but basically you need to create a small 16x16 version of your icon as well as the 32x32 icons, the small version should be named the same as the large but with the "-16" prefix. So for example, if you icon is called: mything.gif
then the small version should be called: mything-16.gif