[refactor] break helper classes out into separate files
[fix] don't throw an exception if we're not ready to scale a PDF (because it hasn't been loaded)
[improvement] remove the ability to rotate PDF pages through hotkeys
[refactor] extract CustomStyle, DocumentOutline, TextLayerBuilder, and ThumbnailView from viewer.js
[skip] white-space
[fix] add a fallback style to toolbar and sidebar for IE
[skip] white-space
[fix] allow PDF viewer to work when not all of its expected DOM elements are present
[skip] white-space
[improvement] PDFView.open returns PDFView
[refactor] extract PageView from viewer.js
[improvement] make responding to hot keys optional
[improvement] refactor options to PDFView.open and make rememberViewState optional
[fix] redraw the PDF when changing scale
[skip] white-space and logging