Travis ci

This small changes implements travis continuous integration. In order to make it work:

- Sign up with your github account in travis-ci.org
- On the account settings enable the github hook for your project (SongRequest)

On each commit on master or each commit on PR's, the hook will be triggered and travis will build it. This CI build uses mono only, but I think it helps making sure it does not break in mono.

We could still setup nunit tests, this could be done later.