Apply changes from cms.Modifier immediately

As discussed in the Core software meeting, the cms.Modifier class now modifies the objects immediately if that cms.Modifier was passed to the constructor of the cms.Process instance.
Added ModifierChain

Allow Modifiers to be grouped together in via a ModifierChain
Merge pull request #6296 from Dr15Jones/haveModifierApplyImmediately

Have cms.Modifier apply immediately