GTK+ added support for a -gtk-icon-style property in themes to
enforce a particular icon style. Do the same for shell themes
with an -st-icon-style property, with the same set of possible
values as the GTK+ variant:
'requested' - use symbolic or fullcolor icon depending on the
icon name (default)
'regular' - enforce fullcolor icons
'symbolic' - enforce symbolic icons
https://bugzilla.gnome.org/show_bug.cgi?id=740447
2940ef07e9