.gitignore: Add *.hdr + google_scanned_models + dataset

Also remove `*.png`. This is no longer necessary when the dataset
directory is ignored, and there are some png files (like textures) that
we *do* want to commit.

.gitignore

@@ -1,9 +1,11 @@
 /weights
 *.pyc
 *._
-*.png
 __pycache__
 venv
 .idea
 .DS_Store
 ._.DS_Store
+*.hdr
+google_scanned_models/
+scripts/nvisii_data_gen/output/dataset/