Ongoing: port GUI to use ACE3-GUI libraries

[brittyazel]

I would like to port more and more of the codebase to use the ACE3 libraries, starting first with the Neuron-GUI sub-addon, which currently uses a lot of custom layout and theming. Theoretically if we moved the GUI codebase over to using the ACE3-GUI libraries, we could drastically simplify the codebase and future maintenance.

This is hampered only by my lack of understanding of how to go about doing this. I have no experience working with Ace3.