This makes gnome-software work much better with metadata from SUSE.
Long term the metadata format needs to be nailed down tighter.

Show empty tiles in the category page as well, and replace them
with the real thing when available. We use the size of the
category to know how many empty tiles to put there.

At the same time, show all non-empty subcategories. An arbitrary
minimum size does not really make sense, and we always want to
show the featured category which may be smaller than 4.

Populate the featured and pick sections with empty tiles
initially, so we can fill them in without having things
jump around too much.

If yum holds the lock, we may otherwise ending up not
showing anything for minutes, which is just broken.

We want to use the size when prepopulating grids,
so don't lie about it.

This was somehow forgotten, and worked just by accident.

This will be used to prepopulate grids with empty tiles.

There was no separator below the list. Now there is.

We were setting the hscrollbar_policy twice.

It is a little much to make a ordinary close button of an
informative dialog blue. Just leave it gray.

The listbox was missing a separator after the last list. Instead
of adding that, change to the frame/scrollbar trick we're using
elsewhere to make lists grow a scrollbar only when needed.

The hidden tabs were causing accessibility heartburn.

There focus keeping patch from earlier today introduced a segfault
when going back from app details to the search page - this is the
one case where the previous focus widget gets removed too early.

Avoid this by not repeating the search if the search term hasn't
changed. This also avoids an annoying wait.

At the same time, improve the scrolling handling in the same way
we do on other pages - keep the scrolling position when going
back to the search page, scroll to the top in all other cases.

Some of these were not used at all. Also, remove hardcoded
text color in some places. Now gnome-software looks great
in dark themes as well.

The HighContrast theme is all about, well, high contrast.
Therefore, we should remove our fancy shadows and most other
theming.

GResource allows preprocessing for pixbufs, so lets
use it.

We use @theme_selected_bg_color for the blue 'stamps', so
it only makes sense to use @theme_selected_fg_color for
the text color.

Maintain the previous focus when coming back via the back
button. Keyboard users all over the world love it.

https://bugzilla.gnome.org/show_bug.cgi?id=708492

Otherwise the text for system apps flows all the way to the right
(e.g. for totem), and that looks terrible.

Make both Back and Alt-Left (Alt-Right in rtl) activate the
back button. Keyboard users love it.

http://bugzilla.gnome.org/show_bug.cgi?id=708487

We use the app summary as the accessible description for each
tile. That way, all the information thats visible on the screen
is also available in accessible form.

https://bugzilla.gnome.org/show_bug.cgi?id=708489

We use the app name as the accessible name, and add '(Installed)'
to have an accessible variant of that blue 'stamp'.

https://bugzilla.gnome.org/show_bug.cgi?id=708484

This is more accessible than the throbbing.

https://bugzilla.gnome.org/show_bug.cgi?id=708481