Add borders or lighter shades for nodes in AnimationTree when the Draw Extra Borders editor setting is enabled

[frandmb]

Describe the problem or limitation you are having in your project

Using the OLED theme the nodes in an AnimationTree will not have any visual differentiator. Adding/removing contrast do nothing here on a black base color, it uses a darker shade for other colors if a contrast is set. Tested on 4.3.stable and 4.4.dev7

Describe the feature / enhancement and how it helps to overcome the problem or limitation

An optional border or lighter background would fix it, as this might be present on other sections as well.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

Current:

Possible solution (1px white border on nodes):

How it looks with non-black colors:

If this enhancement will not be used often, can it be worked around with a few lines of script?

not sure

Is there a reason why this should be core and not an add-on in the asset library?

It affects the readability of nodes on an official theme (OLED)