Use .header-title for all #head headings

This commit:

  1. Updates all main templates to use the new `.header-title` class,
     making these titles less disruptively large on mobile devices.
  2. Centers these titles for mobile breakpoints only, re-setting them
     back to left-aligned text for `md-` breakpoints and up.

Note that in `lib/gollum/templates/wiki_contentf.mustache`, the
`.header-title` is not a `#head .header-title`, so it doesn't inherit
all of the new styles added in this commit.

lib/gollum/templates/commit.mustache

@@ -1,6 +1,8 @@
 <div id="wiki-wrapper" class="compare">
   <div id="head">
-    <h1 class="py-4">{{message}}</h1>
+    <h1 class="header-title text-center text-md-left py-4">
+      {{message}}
+    </h1>
     {{author}} commited {{authored_date}}
     <span class="px-2 float-right">commit <code>{{version}}</code></span>
   </div>

lib/gollum/templates/compare.mustache

@@ -1,8 +1,14 @@
 <div id="wiki-wrapper" class="compare">
-	<div id="head">
-		{{>navbar}}
-	  <h1 class="py-4"><span class="f1-light text-gray-light">Comparing versions of</span> {{name}}</h1>
-	</div>
+  <div id="head">
+    {{>navbar}}
+
+    <h1 class="header-title text-center text-md-left py-4">
+      <span class="f1-light text-gray-light">
+        Comparing versions of
+      </span>
+      {{name}}
+    </h1>
+  </div>
 
 {{#message}}
 	<p>{{message}}</p>

lib/gollum/templates/create.mustache

@@ -1,8 +1,11 @@
 <div id="wiki-wrapper" class="create">
-<div id="head">
-	{{>navbar}}
-  <h1 class="py-4">Create New Page</h1>
-</div>
+  <div id="head">
+    {{>navbar}}
+
+    <h1 class="header-title text-center text-md-left py-4">
+      Create New Page
+    </h1>
+  </div>
 <div id="wiki-content" class="create edit">
   <div class="tabnav">
     <nav class="tabnav-tabs" aria-label="Toggle edit or preview mode">

lib/gollum/templates/edit.mustache

@@ -1,8 +1,11 @@
 <div id="wiki-wrapper" class="edit">
-<div id="head">
-	{{>navbar}}
-  <h1 class="py-4">Editing <strong>{{title}}</strong></h1>
-</div>
+  <div id="head">
+    {{>navbar}}
+
+    <h1 class="header-title text-center text-md-left py-4">
+      Editing <strong>{{title}}</strong>
+    </h1>
+  </div>
 <div class="tabnav">
   <nav class="tabnav-tabs">
     <a href="#" id="edit" class="tabnav-tab selected" aria-current="page">

lib/gollum/templates/history.mustache

@@ -1,8 +1,15 @@
 <div id="wiki-wrapper" class="history">
 <div id="head">
-	{{>navbar}}
-  <h1 class="py-4"><span class="f1-light text-gray-light">History for</span> {{name}}</h1>
+  {{>navbar}}
+
+  <h1 class="header-title text-center text-md-left py-4">
+    <span class="f1-light text-gray-light">
+      History for
+    </span>
+    {{name}}
+  </h1>
 </div>
+
 <div id="page-history">
 
   {{>pagination}}

lib/gollum/templates/latest_changes.mustache

@@ -1,8 +1,11 @@
 <div id="wiki-wrapper" class="history">
-<div id="head">
-	{{>navbar}}
-  <h1 class="py-4">{{title}}</h1>
-</div>
+  <div id="head">
+    {{>navbar}}
+
+    <h1 class="header-title text-center text-md-left py-4">
+      {{title}}
+    </h1>
+  </div>
 
 {{>pagination}}
 

lib/gollum/templates/overview.mustache

@@ -1,8 +1,11 @@
 <div id="wiki-wrapper" class="results">
-<div id="head" class="overview">
-	{{>navbar}}
-  <h1 class="py-4">{{title}}</h1>
-</div>
+  <div id="head" class="overview">
+    {{>navbar}}
+
+    <h1 class="header-title text-center text-md-left py-4">
+      {{title}}
+    </h1>
+  </div>
 <div id="overview">
 
 {{#has_results}}

lib/gollum/templates/search.mustache

@@ -1,7 +1,13 @@
 <div id="wiki-wrapper" class="results">
   <div id="head">
     {{>navbar}}
-    <h1 class="py-4"><span class="f1-light text-gray-light">Search results for</span> {{name}}</h1>
+
+    <h1 class="header-title text-center text-md-left py-4">
+      <span class="f1-light text-gray-light">
+        Search results for
+      </span>
+      {{name}}
+    </h1>
   </div>
 
 {{#has_results}}

lib/gollum/templates/wiki_content.mustache

@@ -1,5 +1,7 @@
 <div id="wiki-content" class="px-2 px-lg-0">
-	<h1 class="pt-4">{{page_header}}</h1>
+  <h1 class="header-title text-center text-md-left pt-4">
+    {{page_header}}
+  </h1>
 	<div class="breadcrumb">{{{breadcrumb}}}</div>
 
 	<div class="{{#has_header}}has-header{{/has_header}}{{#has_footer}} has-footer{{/has_footer}}{{#has_sidebar}} has-sidebar has-{{bar_side}}bar{{/has_sidebar}}{{#has_toc}} has-toc{{/has_toc}}">