Wdfn 567 add validation to email address of user feedback

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Description - WDFN 567 Add Validation to Email Address in Feedback Form

This adds an additional pattern match to the standard HTML5 email address validation. The standard match allows the brower's creators to decide the type of validation provided. Some browsers will not check for a '.' since according to the email address standard, there can be addresses with no '.'. In practice these email addresses are very rare so can reasonably be excluded. So an additional regular expression pattern is used to create filter for most common addresses. This pattern will be enforced on all browsers.

After making a pull request

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