Add wercker.yml that defines the build pipeline

This pull requests adds an `wercker.yml` file. Here is what I defined in the `wercker.yml` file.

## Scala box
In the first line of the wercker.yml file you can see that I defined that the build pipeline must be executed with the `pjvds/scala` box. This is an virtual machine that I have created to build Scala and Java projects. It has Scala, OpenJDK7, Maven and SBT installed. I hope we at wercker will share more details on how you can create your own box anytime soon.

## Build pipeline steps
I have add 5 script build steps that just run the code that is specified in the `code` property. The first one simply echo's the version of the tools that are available in the box. The other four simply execute `mvn`.

## Result of this wercker.yml
I have added my fork to wercker. The last successful build can be seen at wercker: [pjvds/Kornel/c0e9680](https://app.wercker.com/#build/51c03e5db5c1c6ab30000908)