User Menu Enhancements

[nilmerg]

In #4096 we had several additional suggestions for the user menu.

We should think again about some of them and how to integrate them.

With Icinga Notifications Web and its desktop notification feature, there is even a relevant use for one: A toggle in the user menu whether notifications are enabled or not. Right now, this is in the user preferences, which is weird.

We may also move the theme mode selection there, just an idea.

Then there is still #4148.