Improve structure of Vendor Decomposition progress chart

Improve structure of Vendor Decomposition progress chart

After a few commits started being proposed, it became clear that, in
order to minimize merge conflicts, or potential errors with hyperlinks,
the structure had to change/improve slightly.

This patch proposes a different structure that aims at addressing
this concern.

Partial-implements: blueprint core-vendor-decomposition

Change-Id: I47ab4f946b88f0e4450908aedb1718d99435ff1d