1. update scala 2.11.4 in build.sbt & .travis.yml. Note: I don't know if we can add scala 2.10.4 to .travis.yml
2. update play-test 2.3.7 & make it be an optional dependency. TODO should we create a silhouette-test module to remove this optional dependency?
3. update com.atlassian.jwt 1.2.3, scala-guice 4.0.0-beta5, akka-testkit 2.3.8
4. split build.sbt:
+ Maven settings into sonatype.sbt. Note: `credentials += ...`  should be placed in userHome/.sbt/0.13/sonatype.sbt, so other contributors will not see the sbt warning
+ Scalariform settings into scalariform.sbt