Bug 921390 - Display operator name for each SIM on the lockscreen of DSDS devices r=alive

https://bugzilla.mozilla.org/show_bug.cgi?id=921390

Typically we show the sim information exactly the same as on a single devices. There are a few special cases when displaying carrier names on DSDS devices:
1. When in airplane mode, we show only one line: 
`Airplane mode`
2. When there is no sim card inserted, we show only:
```
Emergency calls only
(no SIM)
```
3. When there is only one sim card inserted, show only the information of that sim card.
4. We only show "Emergency calls only" with the sim card that has been set as primary sim.