[feat] engines: add German tonline engine (general, news, images, videos) (#6250)

T-Online_ is a German news portal.

It gets its web results from Google, image results from Flickr and videos results
from YouTube.

For images and videos, it additionally returns result from its
news catalog. However, for pagination we have to specify the result
type (e.g. either videos from YouTube or from T-Online), so we use
flickr/youtube there instead of tonline because the tonline results
are usually irrelevant.

searx/settings.yml

@@ -2313,6 +2313,36 @@ engines:
     shortcut: tm
     disabled: true
 
+  - name: tonline
+    engine: tonline
+    shortcut: tol
+    disabled: true
+    inactive: true
+
+  - name: tonline images
+    engine: tonline
+    categories: images
+    tonline_categ: images
+    shortcut: toli
+    disabled: true
+    inactive: true
+
+  - name: tonline videos
+    engine: tonline
+    categories: videos
+    tonline_categ: videos
+    shortcut: tolv
+    disabled: true
+    inactive: true
+
+  - name: tonline news
+    engine: tonline
+    categories: news
+    tonline_categ: news
+    shortcut: toln
+    disabled: true
+    inactive: true
+
   # Requires Tor
   - name: torch
     engine: xpath