Some uncommitted changes from a couple of years ago..
Save OpenGL context info to the scene/json
Fixed some broken signal/slot code
Fixed build with newer flex, fixes #1
Update to GLEW 1.11.0
Prepare glm 0.9.5.4 as replacement for Eigen.

We might miss some Eigen features, but glm fits better for this kind
of OpenGL application.
Replace Eigen with glm and some custom classes.

Maybe this was just waste of time. Also nothing works anymore.
Remove eigen
Fixes after using new math library