NEW FEATURE IMPLEMENTATION - MESSAGE STYLING

Regarding the implementation details, please, refer to the [detailed documentation](https://drive.google.com/file/d/0B3rfkCYLVzfGaWlXemZlWUtKSGs/edit?usp=sharing) of the Message Starring feature's development and [forum thread](https://bitmessage.org/forum/index.php?topic=3388.0).