Investigate dropping OvUI to follow the IMGUI paradigm

[adriengivry]

Problem this feature should fix
While OvUI works fairly well, it adds an abstraction layer that it often not necessary, and require to write more complex code than if the underlying ImGUI library was used directly.

Expected solution
We should look into the IMGUI paradigm, and evaluate whether we should move away from OvUI to using ImGUI directly in OvEditor.

https://github.com/ocornut/imgui/wiki/About-the-IMGUI-paradigm

[maxbrundev]

Definitely, in my opinion the encapsulation is great especially widgets side but the architecture is adding an unnecessary layer of complexity and it's too much event based to update the widgets data.

However the usage of imgui directly into the editor would not be the best choice as it will add some noise especially if later we want to allow users to create custom GUI, I am not sure that it will be cleaner to remove OvUI