Allow fuzzel.ini to be customized

Instead of overwriting the entire fuzzel.ini on each theme change. Theme
changes are made to fuzzel.theme which is then imported by fuzzel.ini

Rationale:
I like to use vim binds for fuzzel and there wasn't a good way to modify
fuzzel.ini without making the end-4 update process complicated.

.config/ags/scripts/templates/fuzzel/fuzzel.theme

@@ -0,0 +1,8 @@
+[colors]
+background={{ $background }}ff
+text={{ $onBackground }}ff
+selection={{ $surfaceVariant }}ff
+selection-text={{ $onSurfaceVariant }}ff
+border={{ $surfaceVariant }}dd
+match={{ $primary }}ff
+selection-match={{ $primary }}ff