Highlight Build menu buttons on hover (again)

[lizzyd710]

We already have the textures made, and this used to be a thing before our big ImGui overhaul, but now they don't highlight when your mouse is over the big category buttons. This is an easy and quick task, since code is already there for showing a tooltip when you hover over the buttons, you would just need to add lines that would change the image/texture back and forth.