Use gluLookAt() for the model-view matrix

Start using gluLookAt() in preparation for eliminating the use of GL
matrix stack API which is deprecated in modern profiles.

Signed-off-by: Pekka Enberg <penberg@iki.fi>
Use Linmath for GL matrix operations

The matrix stack API is deprecated. Use glLoadMatrixf() that will
eventually be replaced with call to glUniformMatrix4fv()...

Signed-off-by: Pekka Enberg <penberg@iki.fi>