Convert VideoModule to VideoBlock.

Some deprecated functionality has been removed:

- Reading data field and transforms being applied in the init() method.
- The source field.
- The source_visible attribute.

cms/static/sass/elements/_modal-window.scss

@@ -424,7 +424,7 @@
       }
     }
 
-    .xmodule_edit.xmodule_VideoDescriptor .editor-with-tabs {
+    .xmodule_edit.xmodule_VideoBlock .editor-with-tabs {
       .edit-header {
         border: 0;
         background-color: $gray-l4;

cms/static/sass/elements/_xmodules.scss

@@ -34,7 +34,7 @@
   }
 }
 
-.xmodule_VideoDescriptor {
+.xmodule_VideoBlock {
   .wrapper-comp-settings.basic_metadata_edit {
     .list-input.settings-list {
       .field.comp-setting-entry {