Viewport: add default set of HDRI images.

These are taken from HDRI Haven (https://hdrihaven.com). Many thanks to
Greg Zaal for creating and releasing them under a CC0 license!

The HDRIs are intended to be used in the Lookdev display mode. With
1K resolution and compression they are not intended for final renders,
but it keeps the file size small and the difference is not noticeable
for lighting.

Command used for compression:
oiiotool %s --ch R,G,B -d float --compression dwab:300 -o output/%s

release/datafiles/studiolights/world/license.txt

@@ -0,0 +1,3 @@
+All HDRIs are licenses as CC0.
+
+These were created by Greg Zaal (HDRI Haven https://hdrihaven.com).