Distinguish four kinds of projects
Distinguish four kinds of projects

There are four kinds of projects in our build:
- Projects compiled only with Scala 2 (dotty-bot, as well as
  dotty-interfaces since it's Java-only)
- Projects that are part of dotty and compiled with Scala 2
- Projects that are part of dotty and compiled with a non-bootstrapped
  dotty
- Dummy projects for scala{-library,-compiler,-reflect,p}, see the
  comment above `commonDummySettings`

They are now distinguished using four sets of settings. The first and
second set are identical but this will change with the next commit.

som-snytt/dotty,dotty-staging/dotty,som-snytt/dotty,som-snytt/dotty,som-snytt/dotty,dotty-staging/dotty,lampepfl/dotty,dotty-staging/dotty,dotty-staging/dotty,lampepfl/dotty,dotty-staging/dotty,sjrd/dotty,lampepfl/dotty,sjrd/dotty,sjrd/dotty,lampepfl/dotty,sjrd/dotty,som-snytt/dotty,lampepfl/dotty,sjrd/dotty