Rudder

We need to upgrade to Scala 2.11 / liftweb 2.6, because Rudder 3.1 is LTS, supported for certainly 12-18 month, but scala 2.10 will be EOL soon, and liftweb 2.5 is no more supported - even for security reason, see #8640.

Moreover, having only scala 2.11 to support for the forseable future would be much simpler for all the build infra and dev teams (the next version, scala 2.12, will be Java 8 only, so we will certainly not use it for the next Rudder major, and perhaps for the next, next).

The change in code is extremelly minimal (some line of dependencies, and 2 lines of codes). Everything tested works fine under 3.1 with scala 2.11 / lift 2.6. There is a change on parent pom, an other on Rudder project.