Use "section" statement as a container

This commit re-introduces the possibility to use the `section` statement as a container ({section {...}}...{/section}).
Since the `macro` property is not mandatory, it is also possible to provide a string argument to the statement ({section "mySectionId"}...{/section}).

This feature is disabled by default. In order to enable it, you need to set an application environment variable:
```
aria.core.AppEnvironment.setEnvironment({
    templateSettings : {
        allowSectionsAsContainers : true
    }
});
```
As there is already a `with` statement in the parent macro, I am not sure if this one is needed (to be tested).

Especially, I think adding or removing this `with` statement may change the behavior in case there is a property on `this` which has the same name as a local variable of one of the nested macros. To be compared with the behavior before we removed compatibility with sections as a container (if you have time, as it is a very specific scenario, which may not worth spending time on...).