refactor: remove databases from code an use schemas instead

All databases are now saved together in the same LNBITS_DATA_FOLDER.
Extensions have to define a schema.yml file for creating the necessary database.

lnbits/helpers.py

@@ -3,12 +3,9 @@ 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
+    def default(self, obj):
+        if isinstance(obj, sqlite3.Row):
+            return {k: obj[k] for k in obj.keys()}
         return obj