Refactor Theme Interface, add Mail stuff

* Add code on Template Interface (usefull to set Mail Template on setup)
* Add MailSender on Website Interface (a string like "Toto TUTU \<toto.tutu@yopmail.com\>")
* Theme back office UI refactoring
* Mail to create User (user account request) is now a Mail from Rbs_Mail module
* Stuff about Mail sending (job, command for mail installation,...)
* Begin work on Mail Editor

:warning: You have to add a new key in your **project.json** for default mail sender : 
``` JSON
{
...
"Rbs":{
		...
		"Mail":{
			"defaultSender": {
				"name":"Admin",
				"email":"noreply@rbschange.fr"
			}
		}
	}
}
```