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 is a WIP for advanced file sharing, but I won't pursue this for now since using symlinks in the file system works for me, and this is adding a ton of complexity I don't want or need right now.
