refactor: use Flask Blueprints to organize extensions

- extensions are now blueprints: keep views, templastes and statics in the same folder
- increase app security using `flask-talisman`
- whenever possible use {{ url_for }} for links between pages
- remove references to non-existing JavaScript code
- add missing favicon.ico

lnbits/helpers.py

@@ -3,14 +3,11 @@ import sqlite3
 
 
 class MegaEncoder(json.JSONEncoder):
-    def default(self, o):
-        if type(o) == sqlite3.Row:
-            val = {}
-            for k in o.keys():
-                val[k] = o[k]
-            return val
-        return o
+    def default(self, obj):
+        if isinstance(obj, sqlite3.Row):
+            return {k: obj[k] for k in obj.keys()}
+        return obj
 
 
-def megajson(o):
-    return json.dumps(o, cls=MegaEncoder)
+def megajson(obj):
+    return json.dumps(obj, cls=MegaEncoder)