It's not worth showing poorly sized desktop screenshots on a phone.

This makes it fit phones.

This makes it work on mobile but not on desktops.

This makes it work on mobile but not on desktops.

This helps it work well on mobile but not on desktops.

This makes it work better on phones but less well on desktops.

Shuffle the layout a bit to better work on phones, but less well on
desktops.

This drops the selection button as well as the action bar containing the
selection actions as the action bar is too wide to fit in a phone and
the actions are not supported by Phosh anyway.

This conflicts with the one from the view switcher.

This makes the header work in both desktops and mobiles.

This prevents the window from being stupidly small.

Make it work well on desktops and phones alike.

Although this isn't the root of the problem, it at least makes the crash go away.

This fixes the issue where background downloads (from the update
monitor) cause error notifications to pile up in the UI, even though the
user didn't initiate any of them.

Fixes: https://gitlab.gnome.org/GNOME/gnome-software/issues/487

Make sure we hide the developer box as well, not just the label that's
inside.