In this commit we add support for some tags which are also called
void-elements according to
http://w3c.github.io/html/syntax.html#void-elements to be parsed by
our template parser and get tagged as singleton_html_tags.
Fixes: #8387.
Not sure why we have `overflow-y: scroll` in `messages` container in
missed messages email template when it is not a fixed width container
but anyway changing it to `overflow-y: auto` seems to be a safe change
as it will remove the ugly looking inactive scrollbar that was being
displayed there besides the `messages` container without changing the
functionality(if any).
YJDave
Aditya Bansal
Harshit Bansal
Rishi Gupta
James Rowan
Vaida Plankyte