Upgrade to latest scala version

The changes are the following:

 * Upgrade to scala version `2.11.2`
 * Upgrade to sbt `0.13.6` and upgrade sbt plugins accordingly
 * Upgrade dependencies (casbah, scalatest, mockito) to latest version
 * Move from old liftweb json library to the new json4s one, using fastest jackson implementation
 * Do not pollute logs with the exception stacktrace when the port file could not be created  

Keeping capability to cross build for oldest scala versions will necessitate a much more complicated build as dependencies are not all cross build. Projects which did not update to scala `2.11.2` could stick with older versions of this library.
Are you sure you don't want to cross compile for anything but the latest? I think some people still use 2.10 at least?