18128: Adds ability to set up initial per-panel visibility.

18128: Adds ability to set up initial per-panel visibility.

If panelStates isn't defined, the default keeps being "show all panels".
If panelStates is defined, but some panel state isn't included, the default
is to set its initial visibility to false. If it is indeed included but
the optional visibility setting isn't defined, by default the panel will
be shown to avoid having to explicitly set visible:true to all panels.

Arvados-DCO-1.1-Signed-off-by: Lucas Di Pentima <lucas.dipentima@curii.com>