Change hardcoded platform name to PLATFORM_NAME

Replace instances of "edX" with the PLATFORM_NAME setting for
"themability" purposes.

lms/templates/registration/password_reset_confirm.html

 {% extends "main_django.html" %}
 {% load staticfiles %}
-{% block title %}<title>Reset Your edX Password</title>{% endblock %}
+{% block title %}<title>Reset Your {{ PLATFORM_NAME }} Password</title>{% endblock %}
 
 {% block headextra %}
   <!--[if lt IE 9]>
@@ -38,7 +38,7 @@
   <section class="passwordreset container">
     <section class="introduction">
       <header>
-        <h1>Reset Your edX Password</h1>
+        <h1>Reset Your {{ PLATFORM_NAME }} Password</h1>
       </header>
     </section>
 
@@ -51,7 +51,7 @@
       <form role="form" id="passwordreset-form" method="post" data-remote="true" action="">{% csrf_token %}
         <!-- status messages -->
         <div role="alert" class="status message">
-          <h3 class="message-title">We're sorry, edX enrollment is not available in your region</h3>
+          <h3 class="message-title">We're sorry, {{ PLATFORM_NAME }} enrollment is not available in your region</h3>
           <p class="message-copy">Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</p>
         </div>