TravisCI support

[JorgeCastilloPrz]

• Added travis.yml config file with basic config to compile and run tests
• Enabled travis support on travis console for the project
• Enabled PR build autocancelation feature on travis to cancel current build if you push a new commit to the same PR before the previous build has finished (that saves a lot of time to the CI system).
• Added some badges to readme including the travis one.

The moment we start adding test frameworks and tests to the build we can iterate over the .travis.yml config file to add the required gradle commands to run them properly, if the test one is not enough.

[JorgeCastilloPrz]

CI is working properly. Can you review and merge @raulraja @jrgonzalezg ?

Thanks 👍

[jrgonzalezg]

Actually gradle build already implies test task