This commit extract the vertical resizing plugin part from the
`website_mail_snippet_responsive` module into its own module, to allow
reusing it easily.
I prefer to remove this code than leaving it there when it does not
work. The removal reason and the actual problem are better documented in
the Known Issues section of the README so other developers get it easier
to work on it.
Right now only able to pick for the backest element in responsive snippets. This allows it for the previous one.
Also allow other elements than divs to be colored.
Responsive is a hard thing in mails, because mail clients usually render very badly everything.
This new module adds a good collection of snippets in a pseudoresponsive manner, that will seem responsive in most cases, although they are not, technically.
Inspired by https://css-tricks.com/ideas-behind-responsive-emails/.
Sergio Incaser
Jairo Llopis
Daniel Gómez-Zurita