updated Observe tab's topic bar
Major refactor, including:
1. Moved to a complete asynchronous request/response cycle for all HTTP requests.
2. Redesigning the Observe/Consumers tab
3. Minor clean up.
improved readability and type-safety
continued refinement and clean up
performance optimizations and removal of redundant code
fixed streaming consumer update issues
fixed issue with negative deltas
bumped the revision to 0.18.9