Bug: Standardize punctuation for feedback messages.

[baldwindc]

Proposed MR for issue #248.

The feedback messages in feedback.coffee are not consistent with regards to punctuation. Some sentences are ended with a period, while others have no ending punctuation mark. This causes inconsistencies with implementing libraries such as https://github.com/antoantonyk/password-strength-meter.

[worc]

i think the intent is supposed to be the other way around. no full-stops at the end of feedback is more flexible.

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