Add loading indicator on topology option change

[jpellizzari]

Missed in #2232

Adds the loading indicator if changing topology options is taking a long time. Otherwise, its a blank screen.

@fbarl Mind taking a look?

[fbarl]

There are actually two more places where we do state.update('nodes', nodes => nodes.clear()) instead of clearNodes(state); they are in actions OPEN_WEBSOCKET and ROUTE_TOPOLOGY. Do you think any of these two should be using clearNodes instead?

[jpellizzari]

@fbarl Nice catch. I added clearNodes to ROUTE_TOPOLOGY, since that is checking for a topology change. As far as I can tell, the OPEN_WEBSOCKETS action is just clearing the cache, so no need to apply the "loading" logic. I left that one as is.