Add coveralls.io code coverage via jacoco.

Enables code coverage reporting upon pull requests etc. using [Coveralls.io](https://coveralls.io/).

![Coverage Badge](https://cloud.githubusercontent.com/assets/291148/4913509/2eca1396-64b3-11e4-8348-ff3a87c9f917.png)
![Coveralls Config](https://cloud.githubusercontent.com/assets/291148/4913511/318f4588-64b3-11e4-8bed-bae01163cd31.png)

Will change the badge url if this is approved :+1: