GUI redesign metaissue

[jonorthwash]

Current major GUI issues I'd like to see solved:

• Does not respect macOS dark theme
• Buttons with custom fonts look a little weird on macOS
• Does not respect gtk theme in GNU/Linux
• No out-of-the-box interface buttons (play/pause, etc.)
• Frame playback is really slow on macOS

There's no easy way to solve these issues using tkinter.

The solution is a complete rewrite of the interface. @calebho and @keggsmurph21 were working on a GUI redesign using React. Will it address these issues, or will an Electron interface look identical on all platforms?

I'm partial to an interface that looks/feels "native" on all platforms. One library that offers this is wxPython.

[jonorthwash]

See also #93.

[jonorthwash]

Superceded by #159