Update play/deps, add sending gauges

The main addition is the ability to send gauges, for example: `Statsd.gauge("some.key", 42)` will send "some.key:42|g" to statsd.

There are also some minor updates that make it possible to build the project from scratch (e.g. sbt-release 0.4 was not found as gseitz' repo was not available).

JFYI: I also pushed this version to maven central (relocated under groupId `de.javakaffee.net.vz.play.statsd`, as I have publish permissions for de.javakaffee at sonatype) with version `1.0.0-rc2`.