This implements the option to choose directories when uploading files via the Web UI (The most important part of #52).
When you choose a directory, its file and sub-directory structure will be maintained.
Tested with the latest Safari, Firefox, and Chrome.
Additionally, the Deno version was updated, which required some accessibility improvements as well.
This implements generating image thumbnails on the fly via ImageMagick WASM, and tells the browser to cache them for a week, making the loading of photo directories much faster when it has many large images.
Closes#12
