Split the long vtkF3DMetaReader class in multiple reader classes.
This allows better management of the reader and introspection. Two new options are introduced: --extensions-list and --readers-list.
F3DReader is the basic class for every file format readers. It must provide information about its name and descriptions, the managed file formats, and must be able to produce either a VTK reader or a VTK importer.
Each F3DReader need to be added to the F3DReaderFactory singleton. To make it simple and automatic, you just have to declare them with a CMake macro. CMake will generate the class F3DReaderInstantiator which automatically instantiates all the reader classes and registers them to the factory. One instance of this class is hold by F3DLoader.