Use application.conf for Slick settings.

- The system properties scala.slick.ansiDump and scala.slick.dumpPaths
  become config keys slick.ansiDump and slick.dumpPaths.

- slick.ansiDump is enabled by default in testkit/test.

- Drivers get their own Config object. This can be used in the future to
  enable driver-specific features that require a certain database
  version or configuration.

Review by @cvogt. Related to #904 (cc @imcharsi)