grub is extremely slow to install/update when /run isn't available and eventually
times out on querying udev.

We'll add this as an option in the UI in a future commit.

Also, use /run/live/medium (this seems to work everywhere,
whereas the previous path depended on how the ISO was mounted..
it worked on real HW but not in VBox during the latest tests).

Pretty useless as it is
If we ever need to bring back configuration we'll do
so using gsettings.

Otherwise it pushes the size of the window.

Draw lines also and enable search.

Don't show it by default to everybody in the UI.

The UI isn't designed to work in fullscreen,
timezone and slideshow are fixed size.

The only place we use an avatar nowadays is in the screensaver and
the DE provides that functionality already.

Also add a slideshow test script

This was moved to systemd

Note: This commit breaks the slideshow. This early in the cycle we just need
the installer to run and these dependencies prevent building the ISO. We'll
fix that in a later commit.

Add optional /@ and /@home subvolume mount-targets for btrfs (to satisfy timeshift btrfs snapshot feature)

When asked the length of a partition, Parted sometimes returns a negative
value.

df is more accurate and more reliable.

This commit prefers the df value when assessing whether or not to
skip partitions which are less than 5MB.

- At the end of the installation, the installer could quit before
showing the restart dialog.

- In expert mode, the installer could continue instead of waiting
on the pause screen.