Updating version switcher url to /dev/_static

[melissawm]

This is a follow-up to napari/docs#139, to make sure all pages point to the updated version switcher URL (which is https://napari.org/dev/_static/version_switcher.json) There are many files touched, but the only change is to the URL of the version switcher.

[jni]

Jesus 😂

@melissawm should I just YOLO and merge this? 😂

[melissawm]

lol yeah, I did a find/replace with vscode (and checked it) so it should be safe 😅