Allow require JS module loading timeout to be configured by an administrator

Require.JS comes by default with a load timeout of 7 seconds, which means that if a dependency of a module is not satisfied in that time (for example, due to a very slow network), the module will not be executed, and some parts of the page using the module may not work.

The property waitSeconds controls this timeout, see https://requirejs.org/docs/api.html#config-waitSeconds.

The idea of this improvement is to allow administrators of a farm to set the value of waitSeconds without having to override javascript.vm in the skin to add a default load timeout. Ideally, an administrator could change the value of the property either in the XWiki configuration files or in the wiki administration. This would solve issues with XWiki instances that are located far away geographically from some of their users.