This is only one step in updating our opengl canvas to Qt 5.

Notes:

opengl notes:

* removed glu and glew, it's incompatible with qopengl
* force 3.2 as minimum to get glFenceSync
* remove shared context widget:

    When multiple QOpenGLWidgets are added as children to the same
    top-level widget, their contexts will share with each other. This
    does not apply for QOpenGLWidget instances that belong to different
    windows.

    This means that all QOpenGLWidgets in the same window can access each
    other's sharable resources, like textures, and there is no need for
    an extra "global share" context, as was the case with QGLWidget.

* set Qt::AA_ShareOpenGLContexts to share contexts across windows: and
comment it out again because it crashes, at least in VirtualBox.

Todo: fix all the trickery in kis_opengl_canvas_p.h to get the various
functions using Qt's function objects, fix all the places where HAVE_GLEW
now is undefined, and get all those constants and functions using Qt.