Put XBlock css and javascript onto the LMS courseware page

This required changing structural XModules to fully implement
student_view, rather than just returning the HTML of their children in a
get_html call.

[LMS-223]
[LMS-1170]

common/lib/xmodule/xmodule/seq_module.py

@@ -9,6 +9,7 @@ from xmodule.x_module import XModule
 from xmodule.progress import Progress
 from xmodule.exceptions import NotFoundError
 from xblock.fields import Integer, Scope
+from xblock.fragment import Fragment
 from pkg_resources import resource_string
 
 log = logging.getLogger(__name__)
@@ -43,12 +44,6 @@ class SequenceModule(SequenceFields, XModule):
         if getattr(self.system, 'position', None) is not None:
             self.position = int(self.system.position)
 
-        self.rendered = False
-
-    def get_html(self):
-        self.render()
-        return self.content
-
     def get_progress(self):
         ''' Return the total progress, adding total done and total available.
         (assumes that each submodule uses the same "units" for progress.)
@@ -66,20 +61,24 @@ class SequenceModule(SequenceFields, XModule):
             return json.dumps({'success': True})
         raise NotFoundError('Unexpected dispatch type')
 
-    def render(self):
+    def student_view(self, context):
         # If we're rendering this sequence, but no position is set yet,
         # default the position to the first element
         if self.position is None:
             self.position = 1
 
-        if self.rendered:
-            return
         ## Returns a set of all types of all sub-children
         contents = []
+
+        fragment = Fragment()
+
         for child in self.get_display_items():
             progress = child.get_progress()
+            rendered_child = child.render('student_view', context)
+            fragment.add_frag_resources(rendered_child)
+
             childinfo = {
-                'content': child.render('student_view').content,
+                'content': rendered_child.content,
                 'title': "\n".join(
                     grand_child.display_name
                     for grand_child in child.get_children()
@@ -98,11 +97,12 @@ class SequenceModule(SequenceFields, XModule):
                   'element_id': self.location.html_id(),
                   'item_id': self.id,
                   'position': self.position,
-                  'tag': self.location.category
+                  'tag': self.location.category,
                   }
 
-        self.content = self.system.render_template('seq_module.html', params)
-        self.rendered = True
+        fragment.add_content(self.system.render_template('seq_module.html', params))
+
+        return fragment
 
     def get_icon_class(self):
         child_classes = set(child.get_icon_class()