This is necessary to actually install the applications (or remove,
in case we want to remove a featured app that didn't go through
packagekit)

https://bugzilla.gnome.org/show_bug.cgi?id=707185

gnome-weather is the tarball, repository and package name,
but the application ID is org.gnome.Weather.Application,
following the new recommendations from last GUADEC.

https://bugzilla.gnome.org/show_bug.cgi?id=707185

https://bugzilla.gnome.org/show_bug.cgi?id=707210

We coming from the hardcoded plugins, instead of packagekit, we
don't know the installed state, so assume the app is available.
Also, increase the priority, so appstream is run after datadir-apps
(which also sets the installed state).

https://bugzilla.gnome.org/show_bug.cgi?id=707185

Need a C style sort function (-1, 0, 1), not C++ (<)

https://bugzilla.gnome.org/show_bug.cgi?id=707185

It's a terrible idea to use predictable names in /tmp, and in
general we don't need to spawn an external binary, we can use
GIO for the same.
Also, improve the thread safety with GOnce instead of GMutex.

https://bugzilla.gnome.org/show_bug.cgi?id=707185

The plugins are all run in worker threads, so shared data structures
must be protected with locks, and initialization must be protected
with GOnce.

https://bugzilla.gnome.org/show_bug.cgi?id=707185

It's possible that no package is found because the application
was installed through a mean different than PackageKit. In that
case we should not set an error, to avoid aborting the entire
plugin transaction.

https://bugzilla.gnome.org/show_bug.cgi?id=707185

This makes it possible to show information for applications installed
in other locations or through systems different from PackageKit
(for example jhbuild or listaller)

https://bugzilla.gnome.org/show_bug.cgi?id=707185

We must only remove the last .desktop, otherwise app IDs in
reverse DNS notation get stripped to the first component.

https://bugzilla.gnome.org/show_bug.cgi?id=707185

Protect with mutexes all the struct members that are accessed from
multiple threads, and make sure that signals handled by the view
are emitted in the main thread.

https://bugzilla.gnome.org/show_bug.cgi?id=707185

The default main context can be iterated only from the default thread
(because it includes Gdk/Gtk sources), so it cannot be used from
threadsafe methods.

https://bugzilla.gnome.org/show_bug.cgi?id=707185

Plugins seem to return a bunch of utter nonsense, currently.
Add some assertions to teach them. This is clearly not something
we can ship, but it at least shows whats wrong. We should fix
the plugins to pass these assertions, and then turn them into
a warning, plus filtering out bad apples.

This allows offline applications to be shown in the software center.

We want plugins to be able to set the ID from other metadata items if required.

No need to construct these widgets manually.

Use a list box instead of a tree view, add separators,
disable selection.

Manage spinner visibility using a stack instead of an overlay.
At the same time, add a 'No results found' text to the search
page.

When going back to the OS updates list, the title needs
to be set back to "OS updates".

Add the shadow back, but only if the text is scrolling.

Arrange things so that we scroll to the top only when switching
pages using the main buttons, not when going back from a category
or app page.

Keep track of the current subcategory on the category page,
and go back to that subcategory when coming back from an app
page.

Future-proof this a bit, by also supporting going back
to an app page - this may be used in the future when we
get 'related' links on the app details page.

Replace the popup dialog we had here with going to the
details page. The improved back button handling lets us
go back to the installed page from there.

Add a stack, so we can go back from an application to the category
to the overview.

With the search entry now being only in the overview, we are
always going back to the overview when exiting search, so
no need to keep a search_back_id.

This makes page up/down work when you get to the page.
Also, scroll the overview back to the top every time.

Grabbing focus to a widget is a little tricky, since it
must be mapped for that to work. Add a utility function
that waits for that to happen.

This doesn't make a big difference, but it is the proper
way to show a window.