[server] add "socket" field into CommandServer::Options
[kernel] commandserver: also listen on unix domain socket.

Implement Session as template class, that support next sockets:
- boost::asio::local::stream_protocol::socket
- boost::asio::ip::tcp::socket

From now we pay attention to all options that we have.
[server] wrap main CommandServer into try/catch.
[kernel] review log levels for all messages.

Changed in:
- Command
- CommandServer