added .travis.yml

I was surprised to see that you do not leverage travis ci yet. So I just quickly set it up.

Seems like the date comparison should be tweaked:
https://travis-ci.org/liip-forks/platform/jobs/11075277#L332

Also running the tests locally on OSX I noticed:
```
1) Oro\Bundle\UserBundle\Tests\Unit\Entity\EventListener\UploadedImageSubscriberTest::testSetKernelRoot
Failed asserting that two strings are equal.
--- Expected
+++ Actual
@@ @@
-'/var/folders/66/gsrsrt3j68dfd9bm7h3j3yn40000gn/T/oro_unit/web'
+'/private/var/folders/66/gsrsrt3j68dfd9bm7h3j3yn40000gn/T/oro_unit/web'

/Users/lsmith/htdocs/OroCRM/platform/src/Oro/Bundle/UserBundle/Tests/Unit/Entity/EventListener/UploadedImageSubscriberTest.php:33
```

We have a hackday at Liip next Tuesday on OroCRM (https://plus.google.com/events/cge3n3ufrfaut4fbvs9rh151vpc). We could look into these issues then.