Email template fixes to body format, variable lists and descriptions, missing variables

[kimcoleman]

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Changes proposed in this Pull Request:

Improved formatting of all email body content.

Brought back email body text localization that was lost.

Removed variables from the displayed list that were duplicates of other preferred variable names.

Improved the consistency of the variable descriptions across all emails for clarity and fewer translatable strings needed.

Resolved issue in the main email class that was not returning a successful response after email send.

Adding variable for !!check_gateway_label!! so this is always pulled from the latest gateway value vs getting hard coded in the site's specific template.

Now loading check gateway instructions in the email class vs. relying on the magic that was populating this in the includes/email.php template.

Added !!refund_date!! to the user and admin refund email templates.

Other information:

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