[enh] google scholar - python implementation of the engine

The old xpath configuration for google scholar did not work and is replaced by a
python implementation.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/settings.yml

@@ -535,25 +535,8 @@ engines:
     #   android: *test_android
 
   - name : google scholar
-    engine : xpath
-    paging : True
-    search_url : https://scholar.google.com/scholar?start={pageno}&q={query}&hl=en&as_sdt=0,5&as_vis=1
-    results_xpath : //div[contains(@class, "gs_r")]/div[@class="gs_ri"]
-    url_xpath : .//h3/a/@href
-    title_xpath : .//h3/a
-    content_xpath : .//div[@class="gs_rs"]
-    suggestion_xpath : //div[@id="gs_res_ccl_top"]//a/b
-    page_size : 10
-    first_page_num : 0
-    categories : science
+    engine : google_scholar
     shortcut : gos
-    about:
-      website: https://scholar.google.com/
-      wikidata_id: Q494817
-      official_api_documentation:
-      use_official_api: false
-      require_api_key: false
-      results: HTML
 
   - name : google play apps
     engine : xpath