users: reword ban notice messages.

* Show the ban length instead of the ban expiration date in ban notices.
* Fix the ban notice to not say "Your account has been temporarily
  banned" when it's a permanent ban.

app/views/users/_ban_notice.html.erb

@@ -1,5 +1,11 @@
-<div class="notice notice-error notice-large" id="ban-notice">
-  <h2>Your account has been temporarily banned</h2>
-  <div>Reason: <span class="prose"><%= format_text CurrentUser.user.active_ban.reason, inline: true %></span></div>
-  <div>Your ban will expire in <%= time_ago_in_words(CurrentUser.user.active_ban.expires_at) %></div>
-</div>
+<% if CurrentUser.user.is_banned? %>
+  <% @active_ban = CurrentUser.user.active_ban %>
+
+  <div class="notice notice-error notice-large" id="ban-notice">
+    <h2>You have been banned <%= humanized_duration @active_ban.duration %></h2>
+
+    <div>
+      Reason: <span class="prose"><%= format_text @active_ban.reason, inline: true %></span>
+    </div>
+  </div>
+<% end %>

app/views/users/_statistics.html.erb

@@ -89,12 +89,13 @@
         <td><%= presenter.permissions %></td>
       </tr>
 
-      <% if user.is_banned? %>
+      <% if user.is_banned? && user.active_ban.present? %>
         <tr>
           <th>Ban reason</th>
           <td>
             <span class="prose">
-              <%= format_text presenter.ban_reason, inline: true %>
+              <%= format_text user.active_ban.reason, inline: true %>
+              (banned <%= humanized_duration(user.active_ban.duration) %>)
             </span>
           </td>
         </tr>