Always dispatch change events on load/opacity/visible changes
Promote dispatchChangeEvent from ol.renderer.webgl.Layer to ol.renderer.Layer
Promote handleLayerRendererChange from ol.renderer.webgl.Map to ol.renderer.Map
Promote renderFrame from ol.renderer.*.LayerRender to ol.renderer.LayerRenderer
Merge pull request #162 from twpayne/canvas-visibility-and-opacity

Canvas visibility and opacity