Rules improvement: filter based on content

Rules make it possible to automate content curation, to automatically bookmark or archive content when it is added.

Until now, available conditions included tags, title, and URL. These conditions are enough for most use-cases, but sometimes it's better to check the article text.

And going forward, a new condition Content includes is available for that purpose.

By adding text to the Title includes, Url includes, or Content includes the respective parts of every article is checked. If it contains the given text, the condition is fulfilled.

If all conditions match, the action of the rule is applied to the article.