Allow passing in host and port for server connect

Allow passing in host and port for calling createConnection, with sensible default values.

Example for local development:

```javascript
var conn = skynet.createConnection({
  "uuid": "742401f1-87a4-11e3-834d-670dadc0ddbf",
  "token": "xjq9h3yzhemf5hfrme8y08fh0sm50zfr",
  "protocol": "mqtt",
  "host": "localhost",
  "port": 3000
});
```

Example using defaults to skynet.im server on port 80:

```javascript
var conn = skynet.createConnection({
  "uuid": "742401f1-87a4-11e3-834d-670dadc0ddbf",
  "token": "xjq9h3yzhemf5hfrme8y08fh0sm50zfr",
  "protocol": "mqtt"
});
```