Tweak: Improved duplicate template error message.

New message: ERROR: Could not read templates configuration: It looks
like you have one or more duplicate entries in your templates.yml file.
Each template path that you define in the templates.yml file needs to be
unique, otherwise toolkit will not be able to resolve which template a
particular path on disk corresponds to. The following duplicate
templates were detected: shot_publish_area_maya,
sh2ot_publish_area_maya:
sequences/{Sequence}/{Shot}/{Step}/publish/maya