* viewer dialog scaffold
* toolbar divider component
* simple error screen
* material module and tooltips
* show file name in the title
* improved settings, simple image viewer
* flex-based image viewer, minor fixes
* ability to switch between viewers
* single viewer for images
* remove MDL from the Viewer component
* remove hardcoded demo shell layout
remove harcoded assumptions on "header" and "main" elements
* rework text viewer, remove MDL dependency
* upgrade 'unknown format' view, remove MDL
* simplify media viewer layout
* simplify image viewer
* clean pdf viewer
* migrate pdf viewer styles to scss
* rewrite pdf viewer host styles in scss
* fix unit tests and cleanup layout
* file viewer service
* viewer dialog supports downloads if url provided
