more refactoring/cleanup
renamed pageToImage function to pageToPixel
got rid of unnecessary stack functions newStackImage,  newStack as stack functionality got pushed up to tools layer
added support for high dpi displays like retina
Phase 3 complete
- Added phase 4 goals to roadmap from backlog
Phase 3 complete
- Added phase 4 goals to roadmap from backlog
removed redundant code between showImage() and enable()
added a queue/history of pending imageIds so we can avoid "jumpyness' that occurs when image loading happens out of order
updated the example imageLoaders to add the imageId to the returned image object
showImage() now resets the viewport to default unless a viewport is supplied to it