fix #2552: ui: allow to collapse notes panel from guest summary

fix #2552: ui: allow to collapse notes panel from guest summary

Allow to collapse and expand the "Notes" panel on the virtual guests
summary panel.

Further add a browser setting to control the default behavior, one
can chose from:
 * expand on show (default)
 * collapse on show
 * collapse if there are no notes

This way users can make slightly better use of the available screen
space for the guest status.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Co-developed-by: Stefan Reiter <s.reiter@proxmox.com>