change naming convention for scala entities

This pull requests does three things:

- Migrate from scala 2.10.2 to 2.10.3.
- Compile scala files along with java ones the `compile` ant task.
- Change the naming convention for scala entities: the scala file for FooEntity is now expected to be named ScalaFooEntity.scala (as compared to of FooEntity.scala previously).

There are two things I'm not sure about:

- Should the patch include changes to the .po files?
- Is the change in `src/lessons/backtracking/BacktrackingExercise.java` correct? It seems to me that the line I removed was redundant, but I haven't found out how to run the exercise to check it still runs.