https://wiki.gnome.org/Initiatives/GnomeGoals/AppMenuRetirementSigned-off-by: Richard Hughes <richard@hughsie.com>

Export the tile color as a defined color instead of hardcoding the exact style,
and allow category tiles to be distinguished from other tiles by CSS.

... as per latest mockups in
https://github.com/gnome-design-team/gnome-mockups-software/blob/master/wireframes/updates-view.png

This ensures that updates downloaded through the update monitor appear
in the UI as well.

Time span of showing upgrade notification was changed
to a week in dd0086e2

Instead adapt the upgrade GsApp in packagekit-upgrade and rpm-ostree
plugins, so that depending on which one is active either one can handle
the upgrade.

This just hardcodes rebasing to ostree://fedora/%s/x86_64/workstation,
where %s is the next available distro version. In the future, we can
hopefully be smarter with contructing the refspec, but this is a start.

When we do background update checks and fail to do a check (e.g. because
there's no network access), don't update the saved timestamp. This
ensures that we:

 a) continue trying to get updates and not give up for the day, and
 b) don't show misleading "Last checked: " text on the updates page on
    first launch when there's no network connection

Fixes GNOME/gnome-software#17

Regression from commit 4447b4a4.

Previously an app without screenshots would show double space below the
description. This was due to the widgets still being visible but having no
content (but having spacing around them).

Previously an app without screenshots would show double space above the
"no screenshots" placeholder image. This was due to the widgets still
being visible but having no content (but having spacing around them).

When the updates page is offline, a "Network Settings" button is shown
and it opens the Network panel in GNOME Control Center. While this is
fine for users that have wired connections, it's not very useful for
WiFi users. Thus, taking into account that most users connect to WiFi
networks, we're changing the button to open the WiFi settings panel
instead.

This is part of more broader commitment Red Hat along with IBM, Google, and
Facebook made in November 2017.

More on this can be found online:

https://www.redhat.com/en/blog/fostering-greater-open-source-development &
https://www.redhat.com/en/about/gplv3-enforcement-statement

(cherry picked from commit 35cea472)