Fixes layout issue where an ad is placed above a figure
Added a test to cover the figure element scenario
Limiting the number of inline ads that can be rendered
Refactored test
Refactored to remove growing number of ad placement rules

Now placing the ad before the target paragraph. This means we don't
have to worrry about what comes after the paragraph, i.e. h2 or figure
Merge pull request #2812 from guardian/ads-in-articles-layout-fixes

Fixes layout issue where an ad is placed above a figure element