Check the text version of an email notification

Preconditions: The XWiki instance has the Mail Sending configured. An user is created and has a valid e-mail address set on its profile. 

1. Login as user (U1)
2. Make sure the entire wiki is followed (on a page, click on Notifications button, select 'Follow entire wiki' and Save)
3. Click on the Notifications bell
4. Click on Settings, in the right side of Notifications menu
5. Select Daily for "Email Frequency" and Standard for "Details of the changes"
6. In the Applications section make sure all Notifications toggles are set to ON (e.g. for Pages, both for "Notification menu" and for "E-mail")
7. Login as Admin
8. Create/update/comment/delete a page
9. Mention the user in a page
10. Like a page
11. Trigger the "Notifications daily email" job from Scheduler.WebHome
12. On the user's (U1) received email, click on "..." (More) > '<> Show original'
13. Search for: Content-Type: text/plain
14. Observe the displayed events under the Event(s) on the wiki: section