Previously, ShellAppSystem only loaded (and cached) the set of
.desktop files from applications.menu and settings.menu, using
the gnome-menus library. The ShellAppInfo structure was
a "hidden typedef" for GMenuTreeEntry.
But we need to support loading an arbitrary .desktop file. Thus,
refactor the ShellAppInfo into a real struct, with a refcount,
and allow it to point to either a GMenuTreeEntry or a GKeyFile.
Also, in the case where we fail to lookup an icon for an
application, ensure we return a 0 opacity texture.
Before, we looked up application data in several ways; the ShellAppSystem
exported just application ids (though it parsed the .desktop files internally),
and we'd create a Gio.DesktopAppInfo object (reparsing the desktop file again),
wrapping that inside a JavaScript AppInfo class, and finally the AppDisplay
would again parse the .desktop file to get the categories.
Also, to look up applications by id previously, we traversed the entire
menu structure each time.
Some qualities such as the NoDisplay flag were not easily exposed in the old
system. And if we wanted to expose them we'd have to change several different
application information wrapper classes.
All in all, it was quite suboptimal.
The theme of this new code is basically "just use libgnome-menus". We do
not call into Gio for app lookups anymore. The new Shell.AppInfo class
is a disguised pointer for the GMenuTreeEntry item.
To fix the caching, we keep a simple hash table of desktop id -> ShellAppInfo.
Add a GConf key for favorites, and API for retrieving them.
Also add shell_app_system_lookup_basename, which we use from
the app monitor to look up WM_CLASS ids.
To avoid loading applications from two different systems, use
ShellAppSystem solely. This unifies the initial load and the
reload.
Extend ShellAppSystem to also load settings/preferences, and
ensure they appear in the search.
