Added module-level .gitignore files.

This is mostly so that we ignore the src/main/resources/git.properties
file that's created by Maven during build, and reflects the
corresponding settings in the adam repository.
[UTILS-3] Migrating Parquet code out of ADAM

Changes in this commit:
* created the bdg-utils-parquet module
* added dependencies (parquet, AWS, Apache HTTPClient) which will be needed for this module
* moved over the contents of org.bdgenomics.adam.parquet_reimpl and io to this module.

The major exception to this last point are the index, RDD, and helper
classes from adam.parquet_reimpl which depend on ADAM-specific model
classes (like ReferenceRegion), in particular, RangeIndex, IDRangeIndex,
ReferenceFolder, and the RDD class which used the IDRangeIndex
specifically.