move prog lang-related classes to a specific package
put the compilation specific logic into singletons representing each language

- C compilation is still broken
- running entities is still to be merged in these singletons
fix a malformed html file (fix #197), sorry
fix the C compilation. That was easier than feared :)
integrate the execution of entities into language singletons
kill a useless pimple
don't test C for that release: it's marked as broken
better separation of Python and ScriptingLanguage. One day, Ruby will become usable
no need to the singleton mess around the scala compiler now that it's used in one file only
typo--
Make every exercises use SimpleBuggles instead of Buggles.

- That way, Python that use the exercise entity instead of
  regenerating a new one will get a SimpleBuggle that behaves correctly
  (fix #121)
- We have to remove the "abstract" keyword of SimpleBuggle and add an
  empty run() method. This in turn forces to add the "override"
  keyword to all scala buggles defined in exercises. We should
  probably add a word about it in the first lesson where it's
  encountered.
- Note that the on disk worlds are also populated with SimpleBuggles.
  It makes it impossible to load worlds with Buggles (that raise
  exceptions). When we need it, we'll improve the file format.
PLM server URL updated
Merge pull request #198 from Cedric-Huguenin/master

PLM server URL updated
get the latest translation and english improvements of JCB, thanks
'ant i18n-update', no manual change
various improvements to the displayed english strings
'ant i18n-update', no manual change
French translation of the engine back to 100%
[+] Call help action modify to send request to play server (need some improvements with toggle)
translate the bindings of the lander world to french