Option to show message at top of all Axiom applications/charts such as before or during upgrades, when there is a known issue, etc...

We aren't sure how feasible this is (especially if the historian is down for an upgrade or something) but it could be helpful if there was a way for an admin to put a message on a banner at the top of each Axiom application/chart (automatically applied to all (even if not using a saved application/chart)) to help with user communication. 

Examples:

• Next Tuesday at 9 AM there will be a Canary upgrade from version x to y 
• We are currently experiencing/aware of  x problem
• Canary is currently down for maintenance/upgrades