add robot tests

- added robot tests: these tests are going through basic functionality of application and they make sure that on production searx will at least start the right way. To test more specific parts of the application there are unit and integration tests.
- added .travis.yml file: @asciimoo, you enable travis (if you choose so) by logging in to travis-ci.org, then go to https://travis-ci.org/profile and turn ON asciimoo/searx. That's it!