Blocklist: Add frontend elements:

- New field in User profile edition to add/remove tags from their blocklist
- This field works as other tag fields, with auto-completion, and a proper list under the textbox
- User must have the right permissions to edit blocklist (either their own or other users')

client/js/controllers/user_controller.js

@@ -89,6 +89,7 @@ class UserController {
                     canEditAvatar: api.hasPrivilege(
                         `users:edit:${infix}:avatar`
                     ),
+                    canEditBlocklist: api.hasPrivilege(`users:edit:${infix}:blocklist`),
                     canEditAnything: api.hasPrivilege(`users:edit:${infix}`),
                     canListTokens: api.hasPrivilege(
                         `userTokens:list:${infix}`