Add front-end error handlers to indicate when data
could not be fetched, which explains an empty table.
Revise back-end error handling to reduce lines of code;
add a central ControllerAdvice class that catches any
HttpStatusCodeException and generates a JSON response.
Change-Id: I434e602a89d05ed4de13cddc31633970aa2c8e5d Signed-off-by: Lott, Christopher (cl778h) <cl778h@att.com>