[iOS]
Twitter: Notify about new tweets
Reddit: Notify about new posts
Default: Notify about new articles
+ Fixes alignment issues in the inspector view
[macOS]
Twitter: Show notifications for new tweets
Reddit: Show notifications for new posts
Default: Show notifications for new articles
This commit:
- adds a `isFeedProvider: Bool` property to `WebFeed`
- if `isFeedProvider` is `true`, the article extractor is disabled on the inspector, hidden from the context menu, and the toolbar button is disabled. Additionally, if `isFeedProvider` is `true`, `isArticleExtractorAlwaysOn` returns `false` and cannot be set to `true`.