Updates to GeoTiff importer.

Fixed bug that did not translate NoData values correctly.
Enhanced by making GeoTiff reader keep GeoTiff data type.
NOTE: Byte GeoTiff files are actually unsigned bytes, which GeoTrellis does not currently support. Byte GeoTiffs are read in typed as Short.
Removed comments and files that were unintentionally added.
Merge pull request #325 from lossyrob/wip/geotiff

Updates to GeoTiff importer