Improve the CIP Testing Project landing page

Issue Background

With the increase of content experienced after the B@D v1.0 release, the landing page is too dense. An improvement is required.

Summarise the actions related content.
Move the detailed description of each action to the CIP Testing project management page.
- Leave the summarised content in the landing page for now.
Add a section on the landing page about the latest release, and include all the current links related with the release in such a section.
- Leave only the immutable ones or those related with the current release. For everything else, point to the releases page.
Add a section of how to participate specifically in the testing project.
Add a list of the main repositories we are working on with a short description of each.