Option to split entity list & components

[alyti]

As titled, I think it might be worth to experiment with layout of the UI, in this case the entities and their relations stay in top half of the window and second half would be dedicated to the components.

[msklywenn]

I implemented that (with two panels though) with a custom version of egui. It's in the bevy-main branch of my fork.

https://user-images.githubusercontent.com/1546678/119365931-bd3ba200-bcb0-11eb-9331-340906c067ef.mp4

I could clean this up and try to PR egui and bevy-inspector-egui if interested.

[jakobhellermann]

I created https://github.com/jakobhellermann/bevy_editor_pls to build a more familiar editor-like UI on top of the inspector, so I think bevy-inspector-egui itself can stay the way it is and bevy_editor_pls can be used for the split layout.