GDALRasterSource resolutions should not change after resample

[echeipesh]

gdal > console
[info] Starting scala interpreter...
Welcome to Scala 2.11.12 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_211).
Type in expressions for evaluation. Or try :help.

scala> import geotrellis.raster.gdal._
import geotrellis.raster.gdal._

scala> import geotrellis.raster.io.geotiff.{AutoHigherResolution, OverviewStrategy}
import geotrellis.raster.io.geotiff.{AutoHigherResolution, OverviewStrategy}

scala> import geotrellis.raster.resample._
import geotrellis.raster.resample._

scala> val rs = GDALRasterSource("/Users/eugene/proj/geotrellis/raster/data/vlm/aspect-tiled.tif")
rs: geotrellis.raster.gdal.GDALRasterSource = GDALRasterSource(/Users/eugene/proj/geotrellis/raster/data/vlm/aspect-tiled.tif,GDALWarpOptions(-of VRT -ovr AUTO))

scala> rs.resolutions
res0: List[geotrellis.raster.CellSize] = List(CellSize(20.0,20.0), CellSize(40.0,39.94082840236686), CellSize(79.7872340425532,79.88165680473372))

scala> val resampled = rs.resample(TargetCellSize(CellSize(25,25)), NearestNeighbor, AutoHigherResolution)
resampled: geotrellis.raster.RasterSource = GDALRasterSource(/Users/eugene/proj/geotrellis/raster/data/vlm/aspect-tiled.tif,GDALWarpOptions(-of VRT -tap -tr 25.0 25.0 -ovr AUTO -te 630000.0 215000.0 645000.0 228500.0))

scala> resampled.resolutions
res5: List[geotrellis.raster.CellSize] = List(CellSize(50.0,50.0), CellSize(100.0,100.0))

The purpose of RasterSource.resolutions method is to inform at what resolution it is safe to read the data to minimize IO.

This conflicts with default behavior of GDAL Warp DataSource which attempts to preserve the number of overviews using the same pixel decimation from the base raster. So in the example above it attempts to preserve 1:2 and 1:4 overviews when the "resample to CellSize(25,25)" is applied to base raster layer.

[pomadchin]

Will make a separate PR with it probably, to decompose it from #3124

[pomadchin]

Closed in #3214