Introduce the Scala programming language to JLM

- embeed the libraries to compile scala in memory as we do for Java
- various cleanups in the java handling
  - protect stuff to do so only for Java, but not Scala
  - Mark some strings as translatable
  - cosmetics and cleanups
- property deal with offsets in SourceFile (Java should be updated to
  rewrite the error messages to take that into account just as scripts
  and scala do)
- Complain if the scala entity is not found. This of course generates
  a lot of upcoming work :-/
start to use 'universe' instead of 'world' where needed
Type rename for consistency with other similar elements
allow to not have BEGIN/END TEMPLATE if there is nothing in there beside of the solution
ExerciseChooser: display successes in all languages, not only java&python
document Scala
use scala to compile the project so that eclipse manages to edit scala files properly
Change turnLeft()/turnRight() to left()/right() in buggles & turtles
Translate all builtins of buggles and turtles to French

- It is now possible to write avance() instead of forward().
- Also, mark some exception messages as translatable.
- Also, further replace turnRight() and friends to right() and friends.
scalaize the very first exercise of the track
rerun po4a (no real change)
sanitize the lessons.welcome sub packages
sanitize some class names: CompilerScala and CompilerJava
this property handling was inverted with what its name induces
document another recent change (+ cosmetics)