This refactors the data handlers into a more standard/understood model-like architecture, to prepare for a new, more robust config system.
It also fixes a problem with creating new Notes and uploading new Photos via the web interface (related to #58).
Finally, it speeds up docker builds by sending in less files, which aren't necessary or will be built anyway.
This is all in preparation to allow building #13 more robustly.
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
