Add TravisCI integration

Add `.travis.yml` and the corresponding badge to the README.

Change-Id: I8be2f64cfbb83f2ffaf837a2136dfbcccb0f1c42
Reviewed-on: https://gerrit.causes.com/28744
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>