Auto Messaging API Sample First draft

Create a simple application that lets developers send a few variations
of notifications such as
1. A conversation with single message
2. Multiple conversations with either single or multiple messages.
The Notifications are extended with the CarExtender class and thus can
be seen either on the emulator or GearHead dash
3. Add README.txt
4. Update the sample to use the latest android-auto-sdk.jar
5. refactor code to only expose the features in the sdk (no multiple partipants)

Bug: 17582488

Change-Id: Ic5d385361dca5e74c8b5e96dbc11fe11cdb421f7