Cleanup: reorganize doxygen modules

- Nest compositor pages under the compositor module
- Nest GUI, DNA/RNA & externformats modules under Blender.
- Remove modules from intern which no longer exist.
- Add intern modules (atomic, eigen, glew-mx, libc_compat, locale,
  numaapi, rigidbody, sky, utfconv).
- Use 'intern_' prefix for intern modules since some of the modules
  use generic terms such as locale & atomic.

intern/itasc/UncontrolledObject.cpp

@@ -1,5 +1,5 @@
 /** \file itasc/UncontrolledObject.cpp
- * \ingroup itasc
+ * \ingroup intern_itasc
  */
 /*
  * UncontrolledObject.cpp