Network selector

[aaadamgo]

Initial load creates a default config. I'm trying to find a way to reinitialise when we change the config (choose a new network).

[fl0rek]

Currently I don't think there's a shutdown method for an already started node. We'll include it in the worker js api

[aaadamgo]

As part of this issue, I've rectified the network tab fields, allowing multiple bootnodes, and also tested Arabica which gave no errors.

To continue this task, I think we should create a default config for each network, which gets switched and populates the fields when you change. This shouldn't take long to complete.