Dehardcode chain name in CLI

[koxu1996]

This PR fixes #155.

1. Added simple endpoint to Kairos server, that returns chain name:

$ curl 127.0.0.1:9999/api/v1/chain_name
"casper-net-1"

2. Introduced optional --chain_name argument for CLI's deposit:

$ kairos-cli deposit --help | grep chain
      --chain-name <NAME>              Name of the chain, to avoid the deploy from being accidentally included in a different chain

NOTE: Help text is based on casper-client.

In case chain name is not provided, CLI will query server for it.