Make sure the Visual Script submenus/popups don't open in separate window

**Godot version:**
`master`

**OS/device including version:**
all

**Issue description:**
Visual Script submenus/popups open in separate window



**Steps to reproduce:**
one of the many, Right click on the visual script.

**Cause:**
(I believe it's because) We use AcceptDialogs by default for just about everything in VisualScript. Except some edge cases like right clicking on variables opens a PopupMenu.

**ASIDE**

Part of godotengine/godot-visual-script#37

cc: @fire am I doing something wrong? Cause otherwise visual script it quite broken at the moment.

I will check to make sure if it's not my mistake anywhere, if not I will start on a fix for it in the morning.

Also not sure but there also seem to be some bugs with the Dialogs that open in new window. Should I actually create bug reports for all of them. Or just submit separate PRs while fixing the visual script stuff?