Network: add a 'networks --all' option

This option lists disconnected servers as well as connected servers: e.g.

```
<@Atlas> athemenet: (disconnected), electrocode: (disconnected), exno: x79.exno.net, freenode: morgan.freenode.net, overdrive-irc: io.overdrive.pw, and paradoxirc: (disconnected) 
```