Added Support for minAge and maxAge parameters to the AccumuloScheme

Sorry if this isn't quite right, it's my first pull request. I was looking for a way to use Accumulo with Scalding and came across your cascading source. It does everything I need except support the age-off filter. I've modified and tested it to add minAge and maxAge parameters which cause an ageOffFilter to be attached to the input format.

Please consider adding this change to the original repository.