window-list: use ~/.local/share when looking for apps / icons

The icons in the window list are loaded by parsing the desktop
files for a few variations of the window's app ID in a few known
locations.

Add /.local/share/applications to the list of locations it looks
in, to ensure that apps installed in the user's home directory
are considered as well.

src/panel/widgets/window-list/toplevel.cpp

@@ -663,8 +663,12 @@ Icon get_from_desktop_app_info(std::string app_id)
 {
     Glib::RefPtr<Gio::DesktopAppInfo> app_info;
 
+    // TODO: evaluate getting this programmatically by depending on libxdg-basedir or similar.
+    const std::string home_dir(getenv("HOME"));
     std::vector<std::string> prefixes = {
         "",
+        home_dir + "/.local/share/applications/",
+        home_dir + "/.local/share/applications/org.kde.",
         "/usr/share/applications/",
         "/usr/share/applications/kde/",
         "/usr/share/applications/org.kde.",