Add a banner with configurable message

[omkar-ethz]

Motivation

Similar to the status message banner on LandingPageServer (added in SciCatProject/LandingPageServer#394, updated in SciCatProject/LandingPageServer#397), it would be desirable to have a banner with configurable status message also on SciCat home page (or all pages until the user dismisses it). This would let facilities communicate events / outages.

Example from PSI landing page:

[rkweehinzmann]

We second this request as one can use it to visualize current news and updates.