Rather than scanning all apps for searching, use Ryan's new desktop
file index and the glib support APIs for app searching instead of our
own system.
https://bugzilla.gnome.org/show_bug.cgi?id=711631
Application search results are internally categorized in four sets,
multiple and single prefix matches and multiple and single substring
matches. Each set is currently sorted alphabetically by application
name when concatenating the sets to the final result.
Change the last step to sort each set by usage frequency instead,
which is more likely to favor the most relevant match than
"arbitrary" alphabetic order.
https://bugzilla.gnome.org/show_bug.cgi?id=623372
The two parts were mapping windows to applications, and
recording application usage statistics. The latter part
(now called ShellAppUsage) is much more naturally built on top of
the former (now called ShellWindowTracker).
ShellWindowTracker retains the startup-notification handling.
ShellWindowTracker also gains a focus-app property, which is
what most things in the shell UI are interested in (instead of
window focus).
ShellAppSystem moves to exporting ShellApp from more of its
public API, rather than ShellAppInfo. ShellAppSystem also
ensures that ShellApp instances are unique by holding
a hash on the ids.
ShellApp's private API is split off into a shell-app-private.h,
so shell-app.h can be included in shell-app-system.h.
Favorites handling is removed from ShellAppSystem, now inside
appFavorites.js.
Port all of the JavaScript for these changes.
https://bugzilla.gnome.org/show_bug.cgi?id=598646
