Add support for multiple addresses/api keys per service.

[Former user]

I would like to be able to monitor more than one address from a service.

Say I have two NiceHash wallets or on zpool some of my miners are being paid in XVG while other are being paid in BTC.

Having all of them displayed on the one page would be mighty convenient =).

[James Dimitrov]

Issue #141 was marked as a duplicate of this issue.