Make HookSystem usable in modules

[thmarx]

What if a module is using the HookSystem, currently I see a problem because it is request scope.

Maybe we need global HookSystem for these cases.

[thmarx]

Use HookSystemRegisterExtentionPoint to register callback for hook.

To call a hook, you can use the ThreadLocalRequestContext.get(HookSystemFeature.class).
But that will only work on a request based execution

[thmarx]

This is no easy possible by using the CMSRequestContext in modules.