Blender Git Loki

Review update: Renaming, comments, minor refactor

Review update for comments in D7959. No new feature has been added.
Changes here:

Use PIL_time.h instead of chrono. Use BLI_path_util.h instead of stdio.

Remove redundant `_to_export` suffix from some variables.

Clarify that `object_to_export` is `ob_mesh` to distinguish it from
curves objects later on.

Edited comments.

Change in face normal calculation in one loop instead of three for the
three axes components.

Add const where required.

Not hardcode Blender version but use `BKE_blender_version_string()`.

Add filenames to error messages in file opening.