Godot: Empty control nodes (for example Control) should default to pass the mouse event.

[QbieShay]

Godot version:
11d77386

Issue description:
When creating interfaces, it happened to me quite often to create full screen controls and instantiate other elements inside of this full size controls.
This leads to an unexpected behaviour which is that even an empty control by default stops the mouse.
I would expect this behaviour from a solid Control element(buttons, panels, etc) but not from the 'vanilla' Control node.

This behaviour led me to spend quite some time debugging why some gui functionalities were broken, when it was just the control filtering mouse events

Proposal:
All the empty control nodes (so far i can think only of the base control node) should pass mouse events by default.

[Zylann]

I agree, I went into the same situations. Controls that have no visuals by default should ignore the mouse (Control and some of the Container nodes).

[KoBeWi]

Yeah, the problem is that MOUSE_FILTER_STOP is inherited by pretty much every Control-derived node and none of them change this. So this should be changed for each of these nodes individually, unless there's some possibility to change it only for base class.