Extension: add example extension (#644)

* add example ext files

* remove from extension list

lnbits/extensions/example/__init__.py

@@ -0,0 +1,19 @@
+from fastapi import APIRouter
+
+from lnbits.db import Database
+from lnbits.helpers import template_renderer
+
+db = Database("ext_example")
+
+example_ext: APIRouter = APIRouter(
+    prefix="/example",
+    tags=["example"]
+)
+
+
+def example_renderer():
+    return template_renderer(["lnbits/extensions/example/templates"])
+
+
+from .views import *  # noqa
+from .views_api import *  # noqa