STANBOL-1297: updated required Java version to 1.7. NOTE that the compiler plugin still uses 1.6 what means that the Stanbol Source and binaries will still be compatible to Java 1.6.

git-svn-id: https://svn.apache.org/repos/asf/stanbol/branches/release-0.12@1577074 13f79535-47bb-0310-9956-ffa450edef68