[GEOT-4591] Allow image mosaic to load footprints from per granule shapefiles
merge into refactorized classes: empty mosaic work

ImageMosaicWalker refactorization

add useExistingSchema parameter

minor fix

fix imagepiramyd

fix updateCatalog

fix merge with: empty mosaic

fix usage for ImageMosaicDatastoreWalker. Create a test for UseExistingSchema.

remove unused test

close datastore iterator

fix tests on windows switching to shp file

minor review with some small refactor

improve tests

merge with master