Improved logged-in landing page

[duckinator]

The main problems I have with that page as it is now are:

1. The "Recent Builds" frequently gets dominated by 1 or 2 pull requests and cron jobs.
2. Projects with failed cron jobs get buried in the noise from above. If one PR has 8 failed commits in a row, it's hard to notice the single cron job for a different project mixed in.
3. It would be easier to understand if it was grouped by repo.

1 and 2 can be improved by only showing the latest build for each branch on each repo (the other builds are still available on project pages).

As an example, that would turn this:

Into this:

... and that would free up a lot of space for information about other repos!

Grouping it by repo would make it even better, but I'm not entirely sure what that would look like in practice. Maybe something closer to what the new https://cirrus-ci.com/github/$username looks like?