Various minor changes

Just some minor changes I made while debugging things. I fixed a small mistake, the silhouette shader should correctly work for all mesh groups now (it doesn't use their actual ID now, but makes each group different from all others).

I added "clearBoundingBox()" to clear bounding box from GLC_Mesh. It's useful when mesh is changed and BBox must be forced to update.

The "QGLFunctions glFunctions(this); " stuff is there because there seemed to be a problem compiling on Windows machine - the relevant functions are not part of Windows GL/gl.h!

The updates in "src/viewport/glc_viewport.cpp" simply remove some warnings which don't make any sense for parallel projection (when camera is too close).