Simplify the updates panel

Now we're not using the header and hiding the section header button we can
tidy up the code and split up the listboxes as a new GsUpdatesSection widget
that makes the updates page much more manageable.
1 job for <span class="ref-name">wip/hughsie/auto-updates</span> in 6 minutes and 8 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #66263
build-gnome-software

00:06:08