Add support for Challenge Hound (#924)

* Add challenge hound connection type

* Add config

* Add bridge bindings

* Add reader implementation.

* Obvious renames.

* bit more tidying

* refactor

* fix imports

* fix import

* Start feed reader and recognise service.

* Move to using IDs rather than URLs for better security.

* lint

* Validate that challenge exists.

* Drive-by refactors.

* Add add/remove commands for challenge hound.

* Add challenge hound docs.

* Refactor icons

* add some more activity definitions

* changelog

* cleanup feed work

Author: Half-Shot

changelog.d/924.feature

@@ -0,0 +1 @@
+Add support for Challenge Hound.

docs/SUMMARY.md

@@ -9,6 +9,7 @@
   - [GitLab](./setup/gitlab.md)
   - [JIRA](./setup/jira.md)
   - [Webhooks](./setup/webhooks.md)
+  - [ChallengeHound](./setup/challengehound.md)
 - [👤 Usage](./usage.md)
   - [Dynamic Rooms](./usage/dynamic_rooms.md)
   - [Authenticating](./usage/auth.md)