Provide a way to configure font family for subtitle.

.themes/classic/sass/base/_typography.scss

@@ -4,6 +4,7 @@ $serif: "PT Serif", Georgia, Times, "Times New Roman", serif !default;
 $mono: Menlo, Monaco, "Andale Mono", "lucida console", "Courier New", monospace !default;
 $heading-font-family: "PT Serif", "Georgia", "Helvetica Neue", Arial, sans-serif !default;
 $header-title-font-family: $heading-font-family !default;
+$header-subtitle-font-family: $heading-font-family !default;
 
 // Fonts
 .heading {
@@ -21,6 +22,9 @@ body > header h1 {
   line-height: 1.2em;
   margin-bottom: 0.6667em;
 }
+body > header h2 {
+  font-family: $header-subtitle-font-family;
+}
 
 body {
   line-height: 1.5em;

.themes/classic/sass/custom/_fonts.scss

@@ -7,3 +7,4 @@
 //$mono: "Courier", monospace;
 //$heading-font-family: "Verdana", sans-serif;
 //$header-title-font-family: "Futura", sans-serif;
+//$header-subtitle-font-family: "Futura", sans-serif;