more template updates to rename MITx to edX

lms/templates/module-error.html

 <section class="outside-app">
-  <h1>There has been an error on the <em>MITx</em> servers</h1>
+  <h1>There has been an error on the <em>edX</em> servers</h1>
   <p>We're sorry, this module is temporarily unavailable. Our staff is working to fix it as soon as possible. Please email us at <a href="mailto:technical@edx.org">technical@edx.org</a> to report any problems or downtime.</p>
 
 % if staff_access:

lms/templates/static_templates/server-overloaded.html

 <%inherit file="../main.html" />
 
 <section class="outside-app">
-  <h1>Currently the <em>MITx</em> servers are overloaded</h1>
+  <h1>Currently the <em>edX</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@edx.org">technical@edx.org</a> to report any problems or downtime.</p>
 </section>