Open views naming the retired Snow style on Normal

createView threw on style 'snow', so an embed host or a
show_in_gods_eye_view call holding a view from before Snow was retired
was refused outright, camera and layers included. viewFromParams read
style=snow as the recipient's own style, while the app opened the same
link on Normal.

Both now read a retired style as Normal; truly unknown names still
throw. The retired list moves to a browser-free module shared by the
view API, the share codec and visual settings.

docs/TOOLS.md

@@ -92,7 +92,8 @@ pitch), data layers, visual style, map imagery, and an aircraft, military
 aircraft or satellite to follow. `createView` builds and bounds one,
 `viewToParams` and `viewFromParams` write and read it in the share-link
 format the app restores, and `viewUrl` gives the address that opens it. The
-style names are the ones share links use. Ships cannot be followed from a
+style names are the ones share links use; a retired style (`snow`) is read
+as `normal`. Ships cannot be followed from a
 link yet. An aircraft's `follow` may ask for its cockpit view
 (`cockpit: true`); links cannot carry that and open the app following it.