First state of UI rewrite, reimplemenation of agent status displays

@abnanda1 @DamianEdwards @davidfowl @moozzyk 
The expectation here is that it will only return null if the user has navigated to a page that references an instance that has not yet been loaded into the model. This code path will generally only be hit when the user is drilled down into an agent/worker detail view and refreshes the page