Add console mode

[voanhduy1512]

Hi,

This project is really useful but I don't want to run a web server just to find our nix channel information. This PR allows howoldis run directly in the terminal and print out a nice table

nixos-unstable        1 day      a8c71037e04
nixos-unstable-small  7 hours    95eb2fa40e6
nixpkgs-unstable      17 hours   4756e6ff3b8
nixos-18.03           13 hours   91b286c8935
nixos-18.03-small     14 hours   91b286c8935
nixpkgs-18.03-darwin  1 day      91b286c8935
nixos-17.09           12 days    9e1d8b74706
nixos-17.09-small     6 days     be3ac859fb2
nixpkgs-17.09-darwin  5 days     be3ac859fb2
nixos-17.03           120 days   78e9665b48f
nixos-17.03-small     77 days    2c1838ab99b
nixos-16.09           396 days   25f4906da6
nixos-16.09-small     396 days   25f4906da6
nixos-16.03           449 days   dda40aa8d1
nixos-16.03-small     449 days   dda40aa8d1
nixos-15.09           560 days   3727911
nixos-15.09-small     560 days   3727911
nixos-14.12           997 days   b373bf9
nixos-14.12-small     837 days   c191689
nixos-14.04           1031 days  8a3eea0
nixos-14.04-small     1031 days  8a3eea0
nixos-13.10           1367 days  91e952a

Note: This is a breaking change because of the command line argument.

[domenkozar]

It would be better to make it a separate command, I would imagine most cli options would be different (--port for web, --verbose for cli, etc).

That way we also avoid a breaking change.