Improve of editor design/style using imgui

[PanosK92]

Improving our editor's design using ImGui is a promising avenue, as I've seen several examples where ImGui editors are both functional and visually appealing. Any enhancements we make, even minor ones, would be a positive step.

A possible place to start: https://github.com/PanosK92/SpartanEngine/blob/47ee196b8a879fe7b9eb0d93ac23058f4f219ff4/editor/Editor.cpp#L77C5-L77C5

For inspiration, here are a couple of links to editors with ImGui that showcase what's possible in terms of aesthetics and usability: