Convert prefsdialog and others to use gtkmm/C++ API
@dboles
Submitted by Daniel Boles Link to original bug (#784444)
Description
While idly browsing git, I noticed prefsdialog.cpp contains a lot of calls to GTK+ directly, with a bit of the gtkmm/C++ syntax. I don't know the history of the project, but it looks like this might've been a lift-and-shift from a previous C version of it.
I presume that ideally such code would be converted to use gtkmm? If so, I can work on a patch sometime. I use gtkmm in my current project and contribute the occasional patch to gtkmm/glibmm, so hopefully I'm somewhat qualified. :D