Suggesting a different split of Applicability/Expectations sections for Atomic/Composed rules to get rid of headings "Test Defintion" and "Aggregation Definition"

Deleted some duplicate sections and moved up "Atomic rules list" to match the rule structure outline

Replaced words "aggregate"/"aggregated"/"aggregation" in context of composed rules, so that it is now only used in relation to ACT Data Format (Output Data)

Moved the paragraph "A composed rule defines how the outcomes from its atomic rules are used to determine a single outcome for each applicable test target. ..." from Rule Types section to Applicability for Composed Rules section as per Shadi's and Moe's comments, and deleted paragraph on disabling rules due to accessibility support concerns, since it already differs from what Siteimprove is working on.

Tackling Moe's comment.

#test-applicability changed to #applicability

Change #test-applicability to #applicability

Change #test-expectations to #expectations

Removed rogue line break

Fixed another rogue line break

Remove duplicate "Video elements have an audio description"

Add rule ids to composite rule example.
<ul>
      <li>Video elements have an audio description (video-audio-desc)</li>
      <li>Video elements have a media alternative (video-text-alt)</li>
    </ul>