Roadmap addons for BT 3.8

[remrem]

BlogoText 3.8 will bring some improvements and change for the addons systems https://github.com/BlogoText/blogotext/milestone/4, so here a to do list for convert addons from BT 3.7 to BT 3.8.

• Use the new declarative method (easy)
• Use the new 'public.php' for addons public side functions (easy)
• Convert the addons to use the new/modified core functions from BT 3.8 (medium)
• Convert all addons to use the new content feed injected from the core (medium)
• Update 'compliancy' in addons declaration (easy)

A dedicated branch is created for developping and testing purpose https://github.com/BlogoText/blogotext-addons/tree/POC-3.8

When BlogoText 3.8 will be freezed, I will create a new branche for the addons ready for BT 3.8.

[B4rb3rouss]

Reminder to replace titre_url() by title_url() in addons using it (such as relatedpost)

[remrem]

Update addons to use new 'code' settings when needed.