fixing bugs #2690 and #5617 :
- preventing exception when trying to remove a node which not exist in JCR (SimpleDocumentInstanciator.java)
- adding new method to remove main app's index directory
- adding and using new method to delete all files on server when an app is definitively removed (Admin.java)
- thumbnail was not removed from file server (bad subdirectory name)
- removing some useless methods in FileRepositoryManager.java
fixing bug #5721 : adding scrollbars to window
fixing bug #5827