shell: Update shell.hosts to new dashboard configuration storage.

This takes color and avatar directly from the dashboard configuration,
and uses the name in the dashboard configuration as a cache for the
pretty name of the target host.

Also allow setting of the pretty name via shell.hosts.
shell: New shell.image_editor.
shell: Server appearance edit dialog for dashboard.
shell: Styling for multi-server dashboard list
daemon: Remove support for local avatars.
shell: Fix to make text not overflow the buttons in the hosts list