Implement coherent summarizing of revision/build/test status

Right now we have disparate status values across revisions/builds/tests, and we don't have a uniform way to summarize them onto one value, saying e.g.: "this revision is OK", accumulating all the build and test statuses.

Come up with the logic and the terminology to summarize those.

Start by inspecting the repository's existing revision, build, and test status values and their data definitions. Define the terminology and aggregation rules for one coherent summary value, with completion marked by a consistent status model that can express the combined outcome.

Written by the indexing model from the issue text.