Fix receiving utf-8 characters in media push messages

When receiving a media message via push, that contains unicode characters (e.g. emoji) in the body, the unicode characters are shown as ??.
This is because the received body is converted to a ISO_8859_1 byte array.
I changed it to convert it to a utf-8 byte array and set the encoding appropriately. Then the unicode characters are received correctly.

Message with wrong encoding:
![screenshot_2014-04-21-11-49-26](https://cloud.githubusercontent.com/assets/2340865/2753724/7919787c-c93d-11e3-98c6-9eaec561bed1.png)

Message with my patch applied:
![screenshot_2014-04-21-11-50-11](https://cloud.githubusercontent.com/assets/2340865/2753723/74c62a04-c93d-11e3-86cd-e59a1108d467.png)