Add 'monorepo' flag for addons that use that

[pgengler]

When an addon is in a monorepo (github.com/user/repo/trees/master/...) we should continue to fetch data but should set a flag on that addon. Addons with this flag set will be excluded from the "top % of Github stars" calculation, and eventually the "recent commit" scoring calculation should be changed (for monorepos) to run against the checked-out repo to see if files under the specified portion of the monorepo have been part of a commit in that timeframe.