Connection pool support & 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)
It's used for global parameters that would be a PITA to pass around (ansiDump and dumpPaths change the behavior of logging and toString implementations; logging through slf4j is also global by definition). We can also set default parameters for the driver objects (which are also global) here. You can instantiate your own driver with a different configuration if necessary. Database connections (and pools) from config files are loaded with `Database.forConfig` where you can also pass in an alternate Config.