fix: Improve login, server selection and proxy configuration (#2511)

No potentially malicious URLs referenced in markdown; added
servers stays in server selector list; the currently active server
is visible on the bottom right of smaller screens; a proxy configuration
can be provided now and works; a trailing slash in the added server
is no problem anymore, because it's removed.

FIXES: WEB-193

docs/backend-proxy.md

@@ -20,7 +20,7 @@ const proxyConfig = [
   {
     context: '/api',
     pathRewrite: { '^/api': '' },
-    target: 'http://api.icndb.com',
+    target: 'https://api.chucknorris.io',
     changeOrigin: true
   }
 ];