Add akka cluster status panel

[mtsokol]

Hi!

According to @jczuchnowski's guidelines here's PR for introducing akka-cluster status panel showing members from Akka Management API definition.

Here's example (in top right corner):

Additional panel is enabled when --akka-cluster-status <url> option is provided, and as it's optional component to akka tab it introduced few ifs in the code.

It only shows nodeUid and status as more fields made it obscure in my terminal.

WDYT?

[vpavkin]

Looks great! :rocket:

[mtsokol]

Here's refactor after decision to exclude this to a separate tab. The tab displays all info from Akka Management API definition (except there's no example how roles and unreachable exactly look like so will work on that next week).

Cluster members are fixed as Paragraph widget as List doesn't support multiline item displaying 😕