Purpose: Give the ability to people to directly sign (sic) an email template
without opening the mail composer.
Specifications
* do not display 'email' in activity view: either there are emails and new
display applies, either there aren't any and do not dispaly anything;
* update display of template choice: https://www.awesomescreenshot.com/image/3531694/7f6ac0250009599089ec62b6951a88b4;
* add an "mt 16" between activity and first mail template;
Tests have been updated to new specifications.
This commit is linked to task ID 1872169 and PR #26185.