Cleaning up transform system
rename SceneCanvas.pixels => SceneCanvas.entity
Change "pixel" to "canvas" in SceneEvent
Partial implementation of entity_transform
Add InverseTransform
fixes; scene examples working again
Fixed visual examples
Grid visual works; some artifacts in polar plot.
Reversed grid y-orientation; cell (0, 0) is at top-left.
Made more interesting transform in grid example polar cell.
Avoid bright spots at grid line intersections.
Clean up docstrings, remove old code
fix document pop on entity pop
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
line examples working again
Fixed edge artifacts