Keep PixiJS renderer instance as a module variable

This is caused by the Pixi bug: https://github.com/GoodBoyDigital/pixi.js/issues/181
No way to recreate renderer without errors...
Fix memory leaks connected to resize handlers
Cleanup "onLoad" scripts, reserve that name for interactive onLoad scripts
Remove .modelSetupComplete() call, seems to be unnecessary
Dispatch "modelLoaded" using d3.dispatch, do not store handlers manually