Addition of global server disconnection banner

[oodarluz]

Added server connection service to ping end and display banner on threshold. Paired with xhAppServerHealth config property.

Hoist P/R Checklist

Pull request authors: Review and check off the below. Items that do not apply can also be checked off to indicate they have been considered. If unclear if a step is relevant, please leave unchecked and note in comments.

• [X] Caught up with develop branch as of last change.
• [X] Added CHANGELOG entry, or determined not required.
• [X] Reviewed for breaking changes, added breaking-change label + CHANGELOG if so.
• [X] Updated doc comments / prop-types, or determined not required.
• [X] Reviewed and tested on Mobile, or determined not required.
• [X] Created Toolbox branch / PR, or determined not required.