[Templating] Allows "template" as parameter name

And add a test for "__template__" and "parameters" which are forbidden
to avoid any conflict.
[Templating] Rename $parameters to a less common name
[Templating] $view is a reserved parameter name
[Templating] Keep $parameters and $template for backward compatibility

The passed parameters variable rather than the internal Symfony variable.
[Templating] User class variables to avoid any name collision
[Templating] Unset attribute to avoid wasting memory
[Templating] Unset private attributes to free memory