Simplify Logo requirement from users. (#373)

* Simplify Logo requirement from users.
- Only require 1 logo file, instead of a `small` and `large` one.  Just require `logo`.
- Update frontend sso that primary header logo will ALWAYS be owncast logo.
- User's logo will remain in "user content" area.

* Commit updated API documentation

Co-authored-by: Owncast <owncast@owncast.online>

webroot/js/app-video-only.js

@@ -215,16 +215,13 @@ export default class VideoOnly extends Component {
       isPlaying,
     } = state;
 
-    const {
-      logo = {},
-    } = configData;
-    const { large: largeLogo = TEMP_IMAGE } = logo;
+    const { logo = TEMP_IMAGE } = configData;
     const streamInfoClass = streamOnline ? 'online' : ''; // need?
 
     const mainClass = playerActive ? 'online' : '';
 
     const poster = isPlaying ? null : html`
-      <${VideoPoster} offlineImage=${largeLogo} active=${streamOnline} />
+      <${VideoPoster} offlineImage=${logo} active=${streamOnline} />
     `;
     return (
       html`