Remove lasting deprecation warnings

[MightyCreak]

We've done a huge pass on a lot of deprecation warnings, but there are still 6 left that are a bit harder to fix:

/usr/local/bin/diffuse:7424: DeprecationWarning: Gtk.IconSet.new_from_pixbuf is deprecated
  factory.add(DIFFUSE_STOCK_NEW_2WAY_MERGE, Gtk.IconSet.new_from_pixbuf(p))
/usr/local/bin/diffuse:7424: DeprecationWarning: Gtk.IconFactory.add is deprecated
  factory.add(DIFFUSE_STOCK_NEW_2WAY_MERGE, Gtk.IconSet.new_from_pixbuf(p))
/usr/local/bin/diffuse:7460: DeprecationWarning: Gtk.IconFactory.add_default is deprecated
  factory.add_default()
/usr/local/bin/diffuse:1181: DeprecationWarning: Gtk.ImageMenuItem.new_with_mnemonic is deprecated
  item = Gtk.ImageMenuItem.new_with_mnemonic(spec[0])
/usr/local/bin/diffuse:1188: DeprecationWarning: Gtk.Image.set_from_stock is deprecated
  image.set_from_stock(spec[3], Gtk.IconSize.MENU)
/usr/local/bin/diffuse:1189: DeprecationWarning: Gtk.ImageMenuItem.set_image is deprecated
  item.set_image(image)

It would be nice to definitely get rid of them.

[joyously]

I see Theme parsing errors, in addition to the warnings that you list. Are those related?
I'm on Ubuntu Studio 20.04 with the 0.5.0-rc2 version.

(diffuse:86026): Gtk-WARNING **: 18:28:02.020: Theme parsing error: gtk.css:4:24: The style property GtkRange:slider-width is deprecated and shouldn't be used anymore. It will be removed in a future version

(diffuse:86026): Gtk-WARNING **: 18:28:02.020: Theme parsing error: gtk.css:5:24: The style property GtkRange:stepper-size is deprecated and shouldn't be used anymore. It will be removed in a future version

(diffuse:86026): Gtk-WARNING **: 18:28:02.020: Theme parsing error: gtk.css:129:31: The :insensitive pseudo-class is deprecated. Use :disabled instead.

(diffuse:86026): Gtk-WARNING **: 18:28:02.020: Theme parsing error: gtk.css:130:24: The :insensitive pseudo-class is deprecated. Use :disabled instead.

(diffuse:86026): Gtk-WARNING **: 18:28:02.020: Theme parsing error: gtk.css:162:27: The :insensitive pseudo-class is deprecated. Use :disabled instead.

(diffuse:86026): Gtk-WARNING **: 18:28:02.020: Theme parsing error: gtk.css:163:29: The :insensitive pseudo-class is deprecated. Use :disabled instead.

(diffuse:86026): Gtk-WARNING **: 18:28:02.020: Theme parsing error: gtk.css:183:34: The :insensitive pseudo-class is deprecated. Use :disabled instead.

(diffuse:86026): Gtk-WARNING **: 18:28:02.020: Theme parsing error: gtk.css:205:34: The :inconsistent pseudo-class is deprecated. Use :indeterminate instead.
/usr/local/bin/diffuse:7423: DeprecationWarning: Gtk.IconSet.new_from_pixbuf is deprecated
  factory.add(DIFFUSE_STOCK_NEW_2WAY_MERGE, Gtk.IconSet.new_from_pixbuf(p))
/usr/local/bin/diffuse:7423: DeprecationWarning: Gtk.IconFactory.add is deprecated
  factory.add(DIFFUSE_STOCK_NEW_2WAY_MERGE, Gtk.IconSet.new_from_pixbuf(p))
/usr/local/bin/diffuse:7459: DeprecationWarning: Gtk.IconFactory.add_default is deprecated
  factory.add_default()
/usr/local/bin/diffuse:1181: DeprecationWarning: Gtk.ImageMenuItem.new_with_mnemonic is deprecated
  item = Gtk.ImageMenuItem.new_with_mnemonic(spec[0])
/usr/local/bin/diffuse:1188: DeprecationWarning: Gtk.Image.set_from_stock is deprecated
  image.set_from_stock(spec[3], Gtk.IconSize.MENU)
/usr/local/bin/diffuse:1189: DeprecationWarning: Gtk.ImageMenuItem.set_image is deprecated
  item.set_image(image)

[MightyCreak]

I don't have the GTK warnings here. I am on Fedora 32.

It is possible that, if you have a theme different than Adwaita, there might be some bugs coming from Diffuse source code since the code is pretty old. But there is no gtk.css file in Diffuse source code, so I don't know what could be the source of the warnings.

[joyously]

OK, it's likely something on my system, because 20.04 default looked terrible and I struggled with how to make it look more like I had it on 16.04. The new one doesn't have the same Theme choice settings control, so it seems like they have the themes but they are old so they don't let you choose. But I put the name of the theme I was using into the config file.
Carry on...

[MightyCreak]

I still don't get the warnings, I guess it's been fixed somehow.. If we get them back we'll reopen a new issue.