Fixed nginx default server template

- now 'default_server' is correctly placed in the "listen" line instead
of being shoved into "server_name";

- you can provide "listen" variable either as one value, or a list; in
case of a list, each line is pasted into configuration "as is";

- template tries to determine if current server should be the default
server, if you want to avoid that, provide your "listen" value as one
element of a list;

- also list of additional server names ("alias"), can be provided as
a list, in that case it's pasted into template "as is";