Maintenance mode when database connection lost

[martinheppner]

When the database connection is lost an error message is shown - see screenshot.

Instead of this error message, the maintenace mode should be activated in Header.js (see below)

if (totalTours==0) {
return <Box className={"header-container"} style={{backgroundImage: backgroundImage}}>
<Box className={"header-text"}>
<Box sx={{display: "flex", alignItems: "center", marginBottom: "16px"}}>
<img src={/app_static/img/logo-white.png} height={"16px"} width={"29px"}/><Typography style={{fontSize: "16px", color: "#FFF", lineHeight: "16px", marginLeft: "5px"}}>{getDomainText()}

<Typography variant={"h1"}>
{t('start.wartungsmodus')}



}