There should be a preference to set the default loading of js (deferred vs non-deferred)

Since the implementation of XSKINX-35, the default loading of javascript is deferred. This breaks backwards compatibility for existing applications, since before that the scripts were loaded non-deferred. Indeed, there is a parameter to pass to the loading, which can force non-deferred loading, but this parameter implies modifications (sometimes substantial) in existing application.
Depending on how an application is written, deferred loading can cause a big number of bugs.

This can be easily fixed by using a preference setting for the default value, where non-deferred can be set wiki wide.

The existence of such a preferences ensures smoother upgrades, where this optimization can be opted-out, if it causes trouble.

I propose the name:

skinx.deferred.default

for this parameter.