Before this patch, when a user dragged a fixed snippet on the email body, the result had some attributes that are internally used in Odoo to know if you are replacing a part of a view, and which.
This made that editing the placeholders changed directly the snippet template itself.
On other cases, when this addon was removed and then reinstalled, it made that previous templates raise a MissingError when saving any changes on them.
Chances are that if you have (maybe unnoticedly) hit this bug, you have some snippet XMLID from this addon marked as `noupdate=1`, so the recommended upgrade path is to uninstall this addon and reinstall it.
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/.
Jairo Llopis
Daniel Gómez-Zurita