Skip polygon tests on py3
Corrected py3 test skip
Imitial import of glagg line visual from Rossant and Rougier.
Renamed LineAggVisual to LineAgg
Add line_agg examples
line_agg visual is working
Updates to scene/line_agg example
Update example locations
Agg line shows in ViewBox
Fixed gloo.Shader to ignore commented variable declarations