Add ids to settings headings to allow links to sub-sections

Fixes #638

tildes/tildes/templates/settings.jinja2

@@ -9,7 +9,7 @@
 
 {% block content %}
 <section class="settings-section">
-  <h2>Display settings</h2>
+  <h2 id="display-settings">Display settings</h2>
 
   <ul class="settings-list">
     <li>
@@ -70,7 +70,7 @@
 </section>
 
 <section class="settings-section">
-  <h2>Site behavior settings</h2>
+  <h2 id="site-behavior-settings">Site behavior settings</h2>
 
   <ul class="settings-list">
     <li>
@@ -204,7 +204,7 @@
 </section>
 
 <section class="settings-section">
-  <h2>Notification settings</h2>
+  <h2 id="notification-settings">Notification settings</h2>
 
   <ul class="settings-list">
     <li>
@@ -253,7 +253,7 @@
 </section>
 
 <section class="settings-section">
-  <h2>Account settings</h2>
+  <h2 id="account-settings">Account settings</h2>
 
   <ul class="settings-list">
     <li>