RimbleUtils - return URL as network name for custom networks

[MikeLockz]

Is your feature request related to a problem? Please describe.
As noted in a comment in PR #20 we should use the URL instead of the word 'custom' for ethereum networks that don't match an ID.

Describe the solution you'd like
When a network ID does not match with mainnet or any testnets, use the current network URL as the network name.

Additional context
This would also help with internationalization as we would not need to translate each network name.