Make scene inheritance feature and adding scene feature to another more discover-able

[Jeremi360]

I think it is hard to find out that in godot,
you can add scene like a node to current scene or that use scene inheritance.
Even for me advanced user that use godot since version 2.x
I know I can use those features, but keep forgetting ever it is in UI.

This is mostly because of this chain icon used for this

this don't tell user what it dose at all,
its icon should be look like scene icon with plus or something like that

[timothyqiu]

Note that there is a "New Inherited Scene..." option in the Scene menu.

For a very long time, I thought that menu item was the only way to create an inherited scene :P

[Jeremi360]

I forgot about that one