Multiple search fixes

* Remove percent-encoding of the search query when calling youtube API, as it
  breaks UTF-8
* Empty search redirects to /search, not /
* Show the fullscreen search "home page" (from #1977) at /search
* Allow 'region=' parameter to be passed to /search
* Other minor fixes

src/invidious/helpers/youtube_api.cr

@@ -79,7 +79,7 @@ end
 def request_youtube_api_search(search_query : String, params : String, region = nil)
   # JSON Request data, required by the API
   data = {
-    "query"   => URI.encode_www_form(search_query),
+    "query"   => search_query,
     "context" => make_youtube_api_context(region),
     "params"  => params,
   }