Restructuring Fluid source files.

fluid/.gitignore

fluid/CMakeLists.txt

fluid/app/Fd_Snap_Action.cxx

fluid/app/Fd_Snap_Action.h

fluid/app/Fluid_Image.cxx

fluid/app/Fluid_Image.h

fluid/app/align_widget.cxx

fluid/app/align_widget.h

fluid/app/fluid.cxx

fluid/app/fluid.h

fluid/app/mergeback.cxx

fluid/app/mergeback.h

fluid/app/shell_command.cxx

fluid/app/shell_command.h

fluid/app/undo.cxx

fluid/app/undo.h

fluid/documentation/CMakeLists.txt

fluid/io/code.cxx

fluid/io/code.h

fluid/io/file.cxx