docs: extensions (#1258)

* docs: process docs to include UX Stories requirement

* docs: include note regarding different environments

* Services init

* Remove unused canny logos

* docs: add ModalService diagram

* docs: GIF of notification

* docs: add ui-services page

* docs: simplify ui services call out in the general services docs

* docs: tips and tricks for UI services

* docs: moar pages

* docs: dialog gif

* docs: services in summary/sidebar

* docs: gif examples at top of dialog and notification pages

* docs: add UIModal gif

* docs: details for Dialog Service

* docs: include usage information for ui modal service

* docs: detailed information about our UI Notification Service

* docs: services diagram

* docs: remove unused links

* docs: services example and image

* docs: stubbing extension pages

* docs: UX Stories --> User Cases

* chore: eslint fix

* docs: extensions overview + diagram

* docs: update extensions in sidebar

* docs: extension skeleton and registration info

* docs: copy of maintained extensions table partial in the extensions folder

* docs: swap out old extensions structure for new

docs/latest/SUMMARY.md

@@ -21,11 +21,18 @@
   - [Extensions](advanced/architecture.md#misc-extensions)
   - [Diagram](advanced/architecture.md#diagram)
   - [Common Questions](advanced/architecture.md#common-questions)
-- [Extensions](advanced/extensions.md)
-  - [Overview](advanced/extensions.md#overview)
-  - [Modules](advanced/extensions.md#modules)
-  - [Registering](advanced/extensions.md#registering-extensions)
-  - [OHIF Maintained](advanced/extensions.md#ohif-maintained-extensions)
+- [Extensions](extensions/index.md)
+  - [Registering](extensions/index.md#registering-an-extension)
+  - [Lifecycle Hooks](extensions/index.md#lifecycle-hooks)
+    - [preRegistration](extensions/lifecycle/pre-registration.md)
+  - [Modules](extensions/index.md#modules)
+    - [Commands](extensions/modules/commands.md)
+    - [Panel](extensions/modules/panel.md)
+    - [SOP Class Handler](extensions/modules/sop-class-handler.md)
+    - [Toolbar](extensions/modules/toolbar.md)
+    - [Viewport](extensions/modules/viewport.md)
+  - [Contexts](extension/index.md#contexts)
+  - [OHIF Maintained](extension/index.md#maintained-extensions)
 - [Services](services/index.md)
   - [Default](services/default/index.md)
   - [UI](services/ui/index.md)