[naver] support video downloads (#7395)

and fix 'date' for posts newer than 24h

- fix naver blogposts directory error for posts created less than 24 hours ago
- add support for videos on naver blogs
- refactor to remove unnecessary imports
- fix video url scraping method
- rework date handling
- rework video extraction
- add 'videos' option
- add test

docs/gallery-dl.conf

@@ -420,6 +420,10 @@
             "username": "",
             "password": ""
         },
+        "naver":
+        {
+            "videos": true
+        },
         "newgrounds":
         {
             "username": "",