The object can be moved in learnsifts using the mouse

The controls are as follow:
- Middle click moves the object towards or away from the camera
- Right click moves the object along the x/y axes of the window
- Pressing X/Y/Z will allow to rotate the objects around its own X/Y/Z axes
  using the left mouse
- X/Y/Z rotations are exclusives
Avoid potential errors when reading a shader
Improve module_glwindow

- Hide implementation details into the cpp

This avoids the need to define LINUX to have the proper structure when
including GLWindow from another project (which can lead to unexpected
behaviors)
Merge pull request #15 from gergondet/topic/ImproveLearnsifts

Improve learnsifts and glwindow