Add postage syncing state on the status screen

[agazso]

Currently the postage syncing can take 1 to 10 minutes, depending if your node manages download the postage snapshot from swarm or if it needs to fetch the individual stamp events from the blockchain.

In any case it would be good to add this on the status screen, so that there is at least some indication that the postage syncing is in progress. It is possible to get this information with the /chainstate endpoint. I marked with an error where I would put this on the status page: