rawdenoise: better user experience for preview image when blending
rawdenoise: apply gaussian blur to preview buffer for a closer visual match
Merge branch 'master' into rawdenoise_preview

Conflicts:
	src/develop/blend.c
	src/iop/rawdenoise.c
Merge pull request #774 from upegelow/rawdenoise_preview

Make preview to closer match main view in case of active rawdenoise and certain blend modes