Travis CI

* adds the minimal _.travis.yml_ for a Java project (convention over configuration: Oracle JDK 7, runs for pushes to all branches of the repository, emails on failures and when fixed again to the committer)
* changed the the JUnit version to 4.11
* adds the module _aura-tests_ for integration tests and simple first JUnit test case (a client that submits a minimal topology, just source to sink, to be run with 4 execution units)
* removes the fixed requirement that machines require 1 GB RAM and uses relatively more of the memory for our buffers to have it run on relatively small machine

with these changes the build passes: http://travis-ci.org/lauritzthamsen/AURA/builds/29127631

changing the memory for buffers was necessary since with the previous configuration, the build didn't pass: https://travis-ci.org/lauritzthamsen/AURA/builds/29074045

the only non-code change that is necessary is authorizing the Travis app for the user/organization, see http://docs.travis-ci.com/user/getting-started/.

for more information on Travis CI including the _.travis.yml_ configuration options, see http://docs.travis-ci.com/.