See https://blogs.gnome.org/hughsie/2018/02/16/ for more details.

Based on a patch by Iain Lane <iain@orangesquash.org.uk>, many thanks.

Factoring it out makes it possible to use the nicely designed error
messages that Allan / Rafal did in other places as well, not just in
GsUpdateMonitor.

This also switches distro upgrade error messages to use the common code,
fixing the error messages to actually show up instead of a non-working
expander in the current error messages.

https://bugzilla.redhat.com/show_bug.cgi?id=1335414

I guess this is technically a UI freeze break, but given we've not actually
shown any of the upgrade UI to the user before Allan decided it would be best
to backport the latest design.

This reduces the delta against master.

This reduces our delta against master.

This reduces the delta to master.

This makes things a bit simpler, removing a lot of duplicated states and adding
a compulsory boolean to GsApp to avoid overloading the kind.

The missing kind has also been converted to using the UNAVAILABLE state instead.

This is the first step to de-duplicating the GsAppKind and AsAppKind.

Resolves: https://bugzilla.gnome.org/show_bug.cgi?id=751776

In retrospect, 'state' was a bad name for this.

This helper function returns a salted hash string that is specific to the
machine and the user.

If upstream changes the screenshot or remote icon content without changing the
URL in the AppData file then we never re-download the new content.

We also don't want to redownload this every time as well, so just invalidate
all the cached content when we change the minor version of gnome-software,
e.g. from 3-16 to 3-18.

In this case the user dismissed the shell dialog, and we want to undo the
trigger that we just set.

If we're using gnome-software in XFCE or KDE then the user can still reboot
manually and take advantage of the offline update service.

In the UI we want to show 'Fedora - Updates' but in the other plugins (like
fedora-provenance) we need to match on the low-level ID.

Previously, we would use "gnome-software/x.y.z" in some requests and
"gnome-software" in others. This commit factors out gs_user_agent() and
switches all soup_session_new() calls to use it, to ensure that the same
user agent is used everywhere.

... and bump glib dep to 2.45.8 for g_autoptr(GString) support.

We still have a few types that don't support g_autoptr(), but very very
close to having everything ported over.

Make sure that gs_stop_spinner() removes the associated fade-in timeout
source as well.

* There's no point in inserting the link the way it was done
* moreover the link was not translatable
* and the order of parameters was wrong anyway, origin_url should be
  fourth not second

We should also use https instead of plain http.

https://bugzilla.gnome.org/show_bug.cgi?id=745080

This allows us to do three things:

 * Simplify the icon loading, and remove a lot of hacks and heuristics used.

 * Split out a plugin to download icons, which allows us to support remote icons
   for non-webapps which we'll use to good effect soon.

 * Simplify the epiphany web-app integration to avoid having two places to query
   application state.

It turns out to have been a major contributor to hard-to-debug
gnome-software crashes. Unlike the rest of GSource, g_source_set_name /
g_source_set_name_by_id are not threadsafe and calling them from a
worker thread can lead to double frees and / or trashed heap.

https://bugzilla.gnome.org/show_bug.cgi?id=736683

Due to an early return code path, the offline update would still remain
in the triggered state even after pressing cancel in the shutdown
dialog. Fix this.