Add the ability to show a notice at the top of every page; this provides
the ability for admins to display a message to visitors in the case of
infrastructure or index data issues. Notices can have an expiry date and
can be disabled and re-enabled if needed. A subset of HTML can be used
for formatting the text, URLs will be made into clickable links, and
four "levels" are supported (info, success, warning and error).
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
