But only one mail will be sent out by MailHost

As since the introduction of Internet Message Post it is more likely that
conflicts happen. Also, this operation is now safe as sending email in
Entity_sendEmail is made transactionally (as the interaction with MailHost
is done through the creation of an activity)

Also, do not try to reprocess the activity if something goes wrong,
as it may spam the user.

1. accept a list of converison server
2. retry in case of network error

/reviewed-on nexedi/erp5!670

/reviewed-on nexedi/erp5!669

And improve when possible their translation

As the symbol is easier to understand.
Also, update the name of the functions, as the notion of "or equals"
doesn't appear currently.

if you push a new release on office.com the url of your app change "[your_app].app.officejs.com/[release_number]. The solution is to change the strating page to [your_app].app.officejs.com by puting the right relative url "../" or "../../" dependting on the manifest.
CAUTION : This relatibve url, as starting point, don't work on an ERP5 instance. Because your app is located to : [instance_url]/erp5/web_site_module/[your_app]

because of Mass Workflow transition which is not optimised yet