Fix link format for main image/embedded images

[ioanaciont]

This PR is part of a bigger story.

Given a Content with uuid A, the top level id should be http://www.ft.com/thing/A

The embeds, mainImage and leadImages

• apiUrl is https://api.ft.com/{endpoint}/A
• the id should be the same as its top level id: http://www.ft.com/thing/A

The apiUrl from the mainImage, leadImages and embeds fields will contain the value of the requestUrl that is returned by content-public-read.

This modification requires some changes to be made by the Next team (the people who are responsible for ft.com). Do not merge this PR if those changes haven't been implemented. Make sure you talk to @davidlintonattheft before trying to merge this.

PRs related to this story:
https://github.com/Financial-Times/content-public-read/pull/35
Financial-Times/api-policy-component#44
https://github.com/Financial-Times/enriched-content-read-api/pull/13
Financial-Times/internal-content-api#28
https://github.com/Financial-Times/unrolled-content-public-read/pull/4

[ioanaciont]

Fix embedded IDs in the API

[coveralls]

Coverage increased (+1.3%) to 80.231% when pulling e2c9cda on fix/embedded-ids-format into 96b98a1 on master.