Widget force a parentElement on its domElement

[valentinMachado]

It's not possible to create a Widget without a parentElement since parentElement is initialized here and then manipulated there. In my case I want to create a widget then use a generic function that will integrate it in the DOM which is not possible without "hacking" (ie give a parentElement then the line after do widget.domElement.remove().

We could keep the actual behavior but just do the difference between undefined and null meaning when its undefined view.domElement is the parent but when it's null no parent is setted.

WDYT ?

[jailln]

In the same idea than #2005 my opinion is that the Widget constructor should not know its parent and it should be resposible to add itself to the parent. I think it should be done in an util method as you want to do it.