[simple theme] replace Image_layout.js with flexbox CS impl.

* drop image_layout.js from simple theme
* move image_layout.js to oscar theme and delete common js dir (since its empty now)
* align top position of image detail modal with bottom position of search header
* use flexbox to display images; row height can be set via @results-image-row-height in defenitions.less
* display span title underneath each image with a max width of 12rem
* increase margin and padding around image article on desktop and tablet
* make article height smaller on phone layout (height of 6rem) to display more content on current view
* remove content from result, if the title and content matches
* use a group that cotains the flex image article, if images are mixed with other categories
* fix pylint issues in webapp.py
* use the default.html result template in unit tests (thanks @return42)

searx/webapp.py

@@ -726,6 +726,9 @@ def search():
     # Server-Timing header
     request.timings = result_container.get_timings()  # pylint: disable=assigning-non-slot
 
+    current_template = None
+    previous_result = None
+
     # output
     for result in results:
         if output_format == 'html':
@@ -762,6 +765,18 @@ def search():
                 else:
                     result['publishedDate'] = format_date(result['publishedDate'])
 
+        # set result['open_group'] = True when the template changes from the previous result
+        # set result['close_group'] = True when the template changes on the next result
+        if current_template != result.get('template'):
+            result['open_group'] = True
+            if previous_result:
+                previous_result['close_group'] = True  # pylint: disable=unsupported-assignment-operation
+        current_template = result.get('template')
+        previous_result = result
+
+    if previous_result:
+        previous_result['close_group'] = True
+
     if output_format == 'json':
         x = {
             'query': search_query.query,