Scala Installations support

Adds a valid, persistent, best-effort scala library bundle setup on classpath after the choice of a scala desired source level in project-scopes compiler options.

Operates by modifying and serializing the scala classpath container.

Does not include scala-installation registry edition yet.
OK for this one, but the previous one (2.10 -> 2.19 -> 2.10) works as intended on 2.10 (what's being tested is setting a consistent CP container for scalaVer, which better work on 2.10).