Collapse boost "aggregators" in the parent group id.

It seems a bit confusing when navigating through the boost-related m2 repo to remember that it is **boms** which actually holds the interesting BOM artifacts and that **boost-boms** is just an intermediate aggregate used during the build.  Same with **boost-boosters** and **boost-runtimes**.. maybe we could collapse these into the **boost-parent**  group id?