feature request: header alert in mobile header

Implement header alert in MobileHeader as in HeaderAside component.
A basic scenario assumes you use adaptive layout with HeaderAside and MobileHeader.

```ts
const props = {
  headerAlert: 'alert'
}
const Layout = isMobile ? <MobileHeader {...props}> : <HeaderAside {...props} />
```
If desktop component has some features, mobile one should also, shouldn't it?