Bump Play Slick plugin to 0.8.0; misc other version bumps

I used your nice Activator Template to test Play Slick 0.8.0. Here's a PR that bumps some versions.

I haven't announced the 0.8.0 release because Play Slick [hasn't made it](http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22com.typesafe.play%22%20AND%20(a%3A%22play-slick_2.10%22%20OR%20a%3A%22play-slick_2.11%22)) to Maven Central yet. If you want to test in the meantime, the artifacts are in [OSS Sonatype](https://oss.sonatype.org/content/repositories/releases/com/typesafe/play/).