Live email notifications on subwiki

Preconditions:
- The Mail Sending should be configured on Main Wiki: Configure Mail Sending
- A local user exists on subwiki and has an email address set in its profile
- Eventually, go to webapps\xwiki\WEB-INF\xwiki.properties and set notifications.emails.live.graceTime = 0 to enable the sending of e-mails instantly. Make sure the line is not commented out (doesn't have an # at the start of it).

1. Login as Admin
2. Create a subwiki
3. Log in as a simple local user on the subwiki (with email address in the profile)
4. Make sure the entire wiki is followed (on a page, click on Notifications button, select 'Follow entire wiki' and Save) (Since XWiki 15.5 RC1 is not followed by default)
5. Click on the Notifications bell in the top right corner
6. Click on Settings, in the right side of Notifications
7. Set "Email Frequency" to Live
8. Make sure all toggles in the Email column are ON
9. Log in with another user or with Admin
10. Create/update/delete a page
11. Comment in another page
12. Mention the used user in the content of a page