Add a message when subsystems correctly shut downed
- Remove useless keyword inline on header defined methods
- Reduce size of doxygen comments
Remove unused variable
Use anonymous bitfields to explicit padding in classes and structs
- Switch to C++11 way to initialize members from header
- Replace empty bodies constructors and destructors with = default
- Add deleted copy/move constructors and copy/move assignment operators
  to classes which had a destructor
- Explicit the keyword virtual in front of destructors, even if
  the virtual is inherited by the base class
Fix for GL viewport for retina displays
Remove default implementations in GUI Interface abstract class