Removes java 7 method usage. Adds jcenter repo for subprojects

Had to add the jcenter repo in order to install locally.
Could have used guava's Longs here but didn't want to introduce guava as a direct dependency.

http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/primitives/Longs.html#compare(long, long)