Mentions in text format notifications uses the accountID

Issue Summary

When mentioning a user, the notifications received in text format uses the AccountID instead of the readable display name. This makes the mention notation unusable in the notification.

Steps to Reproduce

1. As User A, go to Personal Settings
2. Change the Email notifications format from HTML to Text
3. Mention User A in a Jira comment
4. Check the notification email.

Expected Results

The mention should indicate the name of the user being mentioned.

[~UserA]
[~UserA:accountid]

Actual Results

The mention is only indicating the AccountID

[~accountid:xxxxxxxxxxxx]

Workaround

As the receiving user, switch to HTML notifications.