Use JavaSE-1.6 EE for all bundles

There are some usages of method java.lang.String.isEmpty() and
java.util.Deque<E> which are available since 1.6.
Create initial POMs
Add Eclipse Juno's P2 repository
Add Xtext's P2 repository
Rename TypeValidation to TypeValidationTest

...otherwise Tycho Surefire plugin complains about missing tests and
fails the build.
Generate P2 repository instead of (deprecated) update site
Juno-based Target Platform
Ignore Maven's target/ folder
Minimal config for Travis CI