Load Method should always load

[therion86]

Currently, the problem is that if a callable is registered (e.g. in services.php or in a factory), the automatic class loading does not work because it uses the load method of the DI container.

It should be possible to load everything using the load method of the DI container.

It needs to be checked whether the class name is also present in the statics.

The loadCallable function should be removed in the future, but for now it is a method that wraps the load method for compatibility.