Consider migrating to UI files

[bragefuglseth]

It currently seems like all of the app UI is declared in its code. This may work for now, but makes maintenance and refactoring increasingly harder. I suggest looking into GTK's UI file functionality, which lets you declare interface layouts with XML instead of manually creating each element.

[giantpinkrobots]

The code is actually starting to get kind of unmanageable. I have not used UI files before, though, so I'd have to learn about them beforehand.