Ignore autogenerated files by Activator.
Change the check level of scalastyle from warning to error.

To check style errors on Travis, the check level must be changed to error.
Otherwise "sbt scalastyle" command exits with 0 instead of nonzero exit code.
Check style errors before running tests on Travis.

Run tests only if there is no style errors.
Respond to ping with pong.

ping/ is used to health check the status of a server.