Support content for customization in offline mode

When the Agent is in Offline mode, it defaults to a default color scheme and all customizations are removed. The default grey default background makes it difficult to read icon wording. It would be beneficial for the Agent to either retain locally, the display customizations set on the zone level or, at least, allow the Offline Agent settings to be configured in the Agent.json file so customers can configure the look of the Agent when it goes into Offline mode.