Not all carriers support PDP context ID 1 for data - add others

The default chat script configures APN context ID 1 only and passes that to the dialing command. Not all carriers support data on context ID 1:

See

https://github.com/hologram-io/hologram-python/blob/develop/Hologram/Network/Modem/chatscripts/default-script#L18-L19

```
OK AT+CGDCONT=1,"IP","hologram"
OK ATDT*99***1#
```

It would be ideal to also support other context IDs, e.g. 3.
