updated stylesheet, added link for dev and upgraded for hugo 0.57

data/sidebar/links/hellug.json

@@ -1,6 +1,7 @@
 [
     {"name": "Hellug Wiki", "url": "https://wiki.hellug.gr"},
     {"name": "Hellug Forum", "url": "https://forum.hellug.gr"},
+    {"name": "Hellug Dev Platform", "url": "https://dev.hellug.gr"},
     {"name": "Photos", "url": "https://photos.hellug.gr"},
     {"name": "Λίστες", "url": "https://lists.hellug.gr"},
     {"name": "Αγγελίες", "url": "https://ads.hellug.gr"},