PARQUET-94: Fix bug in ParquetScroogeScheme constructor, minor cleanup

I noticed that ParquetScroogeScheme's constructor ignores the provided klass argument.
I also added in missing type parameters for the Config object where they were missing.

Author: Alex Levenson <alexlevenson@twitter.com>

Closes #61 from isnotinvain/alexlevenson/parquet-scrooge-cleanup and squashes the following commits:

2b16007 [Alex Levenson] Fix bug in ParquetScroogeScheme constructor, minor cleanup