0.13.21 — from home to home

The language switch leads to the same material in the other version. It does so by a stable key: an entry, a series or a built-in page has a key shared by all languages, and the `/i/<key>` route turns it into an address in the given language. The stream has such a key too.

The trouble is that the home page often shows the stream — with its own introduction above the grid, but the same view. The view passed the stream key, so the switch on the home page led to the stream address in the other version: from `/` to `/en/stream`, and from `/en` to `/strumien`. A reader who only wanted to change the language ended up on a different page from the one they came from.

Since 0.13.21 the stream view recognises that it is on the home page and then passes no key. Without a key, the switch and the bar offering the other version lead to the home page: from `/` to `/en` and back. At its own address the stream behaves as before.

The recognition goes by the address rather than by a new parameter. No instance has to add anything — the fix works wherever the home page shows the stream.