When run on Review Board 7.1+, the Message of the Day banner will now

make use of the new standard Page Banner UI component, which takes care

of all the presentation of banners. This creates a more consistent look

and helps make this extension more future-proof.
When run on older versions, the banner will continue to handle all

presentation and placement as before.
This is implemented as two entirely separate TemplateHooks. They

calculate similar state, but behave a bit differently under the hood,

particularly with the visibility state.
There's also a new feature allowing administrators to control whether

users can close this banner. This can be turned off if the banner is

something that needs to always be seen (such as important user

instructions, legal notices, outages, etc.).
This will all be for the upcoming 4.0 release.

Tested on Review Board 7.0 and 7.1, with and without the option

for letting users close banners.
Tested the closing and should-render functionality on both.
Inspected the generated HTML and scripts for all verson/setting

combinations.