[Pidgin] #16274: Pidgin tray icons should follow system icon theme

[Pidgin]

#16274: Pidgin tray icons should follow system icon theme
--------------------------------+--------------------------
 Reporter:  T(A)ILS developers  |      Owner:
     Type:  defect              |     Status:  new
Milestone:                      |  Component:  pidgin (gtk)
  Version:  2.10.9              |   Keywords:
--------------------------------+--------------------------
 Pidgin tray icons are currently always using hicolor icon theme, which is
 hardcoded in gtkmain.c:

 {{{
 icon_path = g_build_filename(DATADIR, "icons", "hicolor",
 icon_sizes[i].dir, "apps", icon_sizes[i].filename, NULL);
 icon = pidgin_pixbuf_new_from_file(icon_path);
 }}}

 They should instead follow icon theme, which automatically fallbacks on
 hicolor. See http://standards.freedesktop.org/icon-theme-spec/icon-theme-
 spec-latest.html for the specification and
 https://developer.gnome.org/gtk3/stable/GtkIconTheme.html for the GTK
 implementation.

 At Tails, this facility would greatly help us to implement Windows
 camouflage (https://labs.riseup.net/code/issues/7404).

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Ticket URL: <https://developer.pidgin.im/ticket/16274>
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