Indicator for transport of incoming messages.

Often I have received messages from other TextSecure users who have switched to SMS (as they are on the move) (or similarly they have lost phone network signal, and can ONLY use push). Currently, the only way in which to see the type of the incoming message is via viewing a single message's detail. If the transport changes often, this in impractical, but can be vital in understanding the chances of your own messages getting through.

I have implemented (partly to familiarize myself with the TextSecure code base) a solution which allows a user to decide how they would like this information to be displayed (if at all).

There is a new preference with 3 options:

![2014-06-27 19 23 31](https://cloud.githubusercontent.com/assets/3319932/3416920/28879f04-fe32-11e3-89c0-e6da006c20dd.png)

The default option, "None", is to leave it as it currently is, with no indication.

These are what the other two options look like:

![2014-06-27 19 23 41](https://cloud.githubusercontent.com/assets/3319932/3416921/2888a7aa-fe32-11e3-8023-3229f3115096.png)
![2014-06-27 19 23 51](https://cloud.githubusercontent.com/assets/3319932/3416922/288f2bfc-fe32-11e3-81da-8755a9d0839e.png)
![2014-06-27 19 24 04](https://cloud.githubusercontent.com/assets/3319932/3416923/2891aaa8-fe32-11e3-811a-adec3b2fed88.png)

I'm not sure on the language used in the preferences? This could probably be improved.