Implement notification banner for hst pages

Requirements

• The notification banner is displayed all the time.
• When the page displayed in the site is a hstpage, show icon and text as specified in:
  https://docs.google.com/spreadsheets/d/1GOq_-dztjLmQ6MMpsJoEF6hg8eDFLTrlAKcQgTtLe50/edit?usp=sharing

Rationale

This is a left-over issue: The notification banner was planned to be implemented for both xpages and hstpages, but for hst pages this was de-scoped for 14.3.