Updated FindGLEW.cmake and FindMagnum.cmake from Magnum repository.
Adapted to Magnum changes.
Adapted to Point2D/3D-related Magnum changes.
Include cleanup.
Don't use namespaces where not absolutely necessary.

It was originaly for Doxygen to have crosslinking in code, but hurts
code readability badly, so removing it.
Update shader to be consistent with the rest.
Removed unnecessary headers.

They only make the code look bigger, nothing else.
textured-triangle: fixed example documentation.
Split function declarations and definitions.

Shorter lines (and less indentation) are better.
viewer: use Vector3::angle() instead of homemade solution.
Added QtCreator stuff to .gitignore.
Adapted to Magnum changes (own type aliases).