[Test] Setup Travis

[olivernybroe]

We need a setup for running automated tests.
Right now we don't really have any tests, but having the environment build up for it beforehand would be nice.

We need a Travis setup which is able to run tests written with IntelliJ's LightPlatformCodeInsightFixtureTestCase.java testing class.

A dummy test using it will be fine, don't bother with writting the test, this issue is only about creating a Travis file which can actually run this without any problems.

Once the commit is there I'll add it in Travis so it actually tests it

Examples of projects using it:
https://github.com/hsz/idea-gitignore
https://github.com/psliwa/idea-composer-plugin
https://github.com/Haehnchen/idea-php-symfony2-plugin
https://github.com/Haehnchen/idea-php-toolbox

Info about their testing:
https://www.jetbrains.org/intellij/sdk/docs/basics/testing_plugins.html

[Bigocb]

I’d like to take this on for hacktober