Apps: create cpp folder for cpp apps

* Want an app directory like this:
     * app
          * cpp
               * SConscript
          * java
               * SConscript
          * python
               * SConscript
* The Sconscript in app will call each SConscript (in cpp, java, and
python).
Apps: create java folder for java apps

* Update jTranscoder app to fit to the package name and an existing
avTranscoder class.
* Comment the line which calls the Sconscript of java apps from
SConstruct (need several builds to generate class files of java
apps...need to find something better).
Sconscript of src: refactoring

Move how to generate JAR before install instructions.
Sconscript: put Jar in a directory when build it
Merge pull request #68 from cchampet/build_organize_apps

Build: organize apps