Change url in comments, decorate approach (#431)

* WIP: url mapper, wrapped reader approach

* create url mapper on start

* add pattern matching in mapper

* check pattern matching in test

* change site-id from radio-t to remark42 in tests

* create new url mapper on demand, based on given func, union strict and prefix rules

* rename convert to remap

* add import with mapper test

* rename mapper func to UrlMapperMaker, create comments in test via data service

* move /import/wait to /wait ctrl

* add remap cmd

* fix url naming

README.md

@@ -769,7 +769,14 @@ _returned id should be appended to load image url on caller side_
 * `GET /api/v1/admin/export?site=side-id&mode=[stream|file]` - export all comments to json stream or gz file.
 * `POST /api/v1/admin/import?site=side-id` - import comments from the backup, uses post body.
 * `POST /api/v1/admin/import/form?site=side-id` - import comments from the backup, user post form.
-* `GET /api/v1/admin/import/wait?site=side-id` - wait for import completion.
+* `POST /api/v1/admin/remap?site=side-id` - remap comments to different URLs. Expect list of "from-url new-url" pairs separated by \n. 
+From-url and new-url parts separated by space. If urls end with asterisk (*) it means matching by prefix. Remap procedure based on
+export/import chain so make backup first.
+    ```
+    http://oldsite.com* https://newsite.com*
+    http://oldsite.com/from-old-page/1 https://newsite.com/to-new-page/1
+    ```
+* `GET /api/v1/admin/wait?site=side-id` - wait for completion for any async migration ops (import or remap).
 * `PUT /api/v1/admin/pin/{id}?site=site-id&url=post-url&pin=1` - pin or unpin comment.
 * `GET /api/v1/admin/user/{userid}?site=site-id` - get user's info.
 * `DELETE /api/v1/admin/user/{userid}?site=site-id` - delete all user's comments.