reenabled ViewManager displaymode modal show/hide including animations

[dominikg]

had to add showModal/hideModal to ViewManager, as the functionnames show/hide (where this was done before we switched to widgets) are now reserved for widget use.

there might be an easier solution and animateModal shares a good bit of code with animateLayer (like before).

@Sebastian F:

lets talk about this tomorrow please

[fastner]

I'm @fastner :)