AllTray should support scalable icons (e.g., SVG)

Current windowing specifications (see EWMH, ICCCM) specify that each window sets an XPM icon for itself, which is stored in the X Server as a resource. AllTray currently fetches this icon through wnck's get_icon method and uses it in the tray. However, these icons are not scalable and AllTray should use scalable icons (such as SVG icon images) when possible.

There is a window manager hint called WM_ICON_NAME but that refers to the window name (see ICCCM § 4.1.2.2 which states: "The WM_ICON_NAME property is an uninterpreted string that the client wants to be displayed in association with the window when it is iconified (for example, in an icon label).", it is similar to WM_NAME).

With this information the only way to really figure out the application icon (not the window icon) is by caching all .desktop files and find the application icon by matching the values from /proc against the Exec keys. If a .desktop file cannot be found the procedure below may provide a nice fallback mechanism.

  1. Find an icon using the process name (as reported by /proc/$PID/stat{,us} on GNU/Linux or by libgtop)
  2. If that fails, use icon (or mini_icon) provided by libwnck for the application.

This bug depends on bug 382548 being implemented.