Start sbt only if necessary, don't keep server alive
Start sbt only if necessary, don't keep server alive

This commit changes the behavior of the IDE so that it runs
`configureIDE` only if the project hasn't been configured yet. sbt will
now be started only if necessary, and the server will not be kept alive
longer than necessary.

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