Improve connection indicator

[dergigi]

We have a connection indicator already, but it only shows up if the UI can't connect to the API. It currently looks like this:

Once a connection is established, it will look like this:

I'd propose a connection indicator either in the header or the footer, something like a simple green/red dot and some text that says "Connected" or "Disconnected".

[secondl1ght]

I put in a PR for this #55