Edit unpublished template change messages

[momo3404]

Fixes #1261.

Changes proposed in this PR:

• Fix the typo in the message alerting users that their published templates now have unpublished changes.
• Add a message in the Templates section explaining what the pencil icon means on published templates now have unpublished changes.

[github-actions]

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[aaronskiba]

These changes are looking good. I just have one comment regarding some of the conversations the team had about the templates.

We had discussed the issue of the two-steps required with transfer "customisation" + "publish changes". After the first step (transfer customisation), I wonder if it would be worth also rendering a flash message stating something along the lines of "Please select "Publish Template" for these changes to be available to users".