Custom DMSG-Server

[mrpalide]

Feature description Ability to connect to specific dmsg server instead trying to connect dmsg server lists available on http://dmsgd.skywire.skycoin.com/dmsg-discovery/available_servers.

Describe the solution you'd like use some flag like --dmsg-server on starting Skywire by skywire-visor

Describe alternatives you've considered We can set some setting on config file too, but flag is sufficient I think.