Add support for giving a custom exception handler

[ShadoMagi]

This is a simple addition of giving a custom ExceptionHandler to the SprayConfiguration to allow a custom one to be set for the SprayActor. This is a missing feature that allowing it to be overwritten allows nicer failure messages to be returned on exceptions.

[2rs2ts]

Looks like there are scalastyle violations.

[ShadoMagi]

Will fix the scalastyle issues when I add a test. The test is non-trivial to write for this feature :(