Make configurable how window information is formatted in the desktop display.

[cfuehrmann]

Example: The command for "emacs foo.txt" is "emacs foo.txt", while the window title is "emacs@hostname". In this case, it is better to display the command. In certain other cases, it is better to display the window title. The display format should be configurable on a per-command basis, in a configuration file. To avoid introducing yet another self-made syntax, the plan is that the configuration file be OCaml. However, it should be so simple that people without any programming knowledge can adapt it to their needs. So the only noteworthy requirement for changing the configuration is the possession of an OCaml compiler. (Thus our design philosophy is similar to that of xmonad, where the configuration file is written in Haskell.)