Replace `path`s with `dir`s

Specifying exact path isn't useful; they've been replaced with directories (folders), where day-to-day data will save to automatically (instead of specifying anew each time).

config.ini parameters affected: savepath -> savedir, loadpath -> loaddir, imsavepath -> imsavedir. If auto, no behavior changes - else, just strip filenames (e.g. folder/data.csv -> folder/).

.exe release

Added .exe launcher and installer. See config.ini for new features.

No icon since it runs in a browser tab; close via Task Manager. If browser tab is closed, you can reopen by going to the URL, or launching the app again (it won't create a new process if another is running, by default).

Searchable via Windows search ("prodapp").