daemon: Also store name, color, and avatar in dashboard configuration

Reviewed-by: Stef Walter <stefw@redhat.com>
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.

Reviewed-by: Stef Walter <stefw@redhat.com>
shell: New shell.image_editor

Reviewed-by: Stef Walter <stefw@redhat.com>
shell: Server appearance edit dialog for dashboard

Reviewed-by: Stef Walter <stefw@redhat.com>
shell: Styling for multi-server dashboard list

Reviewed-by: Stef Walter <stefw@redhat.com>
daemon: Remove support for local avatars

Closes #1467
Reviewed-by: Stef Walter <stefw@redhat.com>