Create unified "On current desktop" api

Clicking on a url opens it in the web browser window
that last had activity, not the one on the current
desktop. Maybe this is something that the Web
applications could fix.

I would hope that all of these Virtual Desktop tools
support an api that allows applications to ask whether
a window is on the current desktop. If there are no
current windows on the current desktop, the application
could decide to open an new one