Added new error pages and changed textbook image

404.html

@@ -3,5 +3,5 @@
 
 <section class="activation">
   <h1>Page not found</h1>
-  <p>The page that you were looking for was not found. Go back to the <a href="/">homepage</a> or let us know about any pages that may have been moved at <a href="mailto:">mailto:</a>.</p>
+  <p>The page that you were looking for was not found. Go back to the <a href="/">homepage</a> or let us know about any pages that may have been moved at <a href="mailto:technical@mitx.mit.edu">technical@mitx.mit.edu</a>.</p>
 </section>

sass/_textbook.scss

@@ -19,6 +19,7 @@ div.book-wrapper {
 
       div.hitarea {
         margin-left: -22px;
+        background-image: url('/static/images/treeview-default.gif');
 
         &:hover {
           opacity: 0.6;

server-error.html

+<%inherit file="main.html" />
+
+<section class="activation">
+  <h1>There has been an error on the <em>MITx</em> servers</h1>
+  <p>Our staff is currently working to get the site back up as soon as possible. Please email us at <a href="mailto:technical@mitx.mit.edu">technical@mitx.mit.edu</a> to report any problems or downtime.</p>
+</section>

server-overloaded.html

+<%inherit file="main.html" />
+
+<section class="activation">
+  <h1>Currently the <em>MITx</em> servers are overloaded</h1>
+  <p>Our staff is currently working to get the site back up as soon as possible. Please email us at <a href="mailto:technical@mitx.mit.edu">technical@mitx.mit.edu</a> to report any problems or downtime.</p>
+</section>

server_down.html

-
 <%inherit file="main.html" />
 
 <section class="activation">
   <h1>Currently the <em>MITx</em> servers are down</h1>
-  <p>Our staff is currently working to get the site back up as soon as possible. Please email us at <a href="mailto:">mailto:</a> to report any problems or downtime.</p>
+  <p>Our staff is currently working to get the site back up as soon as possible. Please email us at <a href="mailto:technical@mitx.mit.edu">technical@mitx.mit.edu</a> to report any problems or downtime.</p>
 </section>