Blender Git Loki

Fix: Ensure that KeyingSet.bl_description field is properly escaped when using the Export to File operator

Previously, if double-quotes appeared in the KeyingSet.bl_description field,
these would cause a syntax error in the resulting .py script export of the
KeyingSet. Since single quotes are even more likely to appear
(e.g. as apostrophes), we now use triple quotes here.

Unreported bug, noticed earlier when investigating T61010.